How-To: GMT900 Auxiliary Battery Installation.

parshal · September 10, 2009

I installed an auxiliary battery in my '09 Sierra 1500 and thought I'd pass along how I did it so that there's one place to find info for others wanting to do this. There is no aux battery kit for the GMT 900 as there is with the 800. I gathered most of the information off this site from a few posts and PM's with different people. So, thanks to everyone who provided me information and sent pictures. I will post pictures that people sent me, too.

Here are the parts. There have been a few posts here with the parts for the GMT 900 but those lists are incomplete. In addition to the parts below you'll need 7 - 10 feet (overkill but enough) of 18 gauge wire in three colors. I bought mine at Radio Shack for $7 and it had red, green and black.

25876897-CABLE;NEGATIVE AUX BAT

15942730-CABLE;POSITIVE AUX BAT

25862351-CABLE;POSITIVE AUX BAT RH

21021808-NUT - read below for specifics

11609411-NUT - read below for specifics

12135194-RELAY;AUX BAT

15881616-COVER;AUX BAT POS JUNCTION BLOCK

14005061-RETAINER;AUX BAT HOLDOWN

11509853-BOLT;AUX BAT HOLDOWN

19116352-mega fuse holder

15305801-[inline-To Battery Positive Cable Connector]; Aux ; Aux Camper Bat (TP2) ; 4-Way male black; may be listed as O2 sensor connector but it's the same generic connector

13525970-terminal connectors (for X2 connector of the under hood junction box, pins B4 and A5)

For the nuts, you'll use more than two of the brass nuts. These nuts are used to connect cables to the mega fuse holder and relay. You can take some from the factory fuse holder but I still ended up using six. I don't know which part number above is for the brass nuts so you'll need to ask the parts guy. The other two nuts are used on the battery cable posts to connect accessory wires.

Part 19116352 replaces the existing mega fuse holder near the passenger hood hinge. Verify that you have two fuses, 175 AMP for the cable to fuse box and 125 AMP for the aux battery relay cable. I reused the existing 175 AMP fuse. I put the aux battery cable on the second post on the right side with the 125 AMP fuse. I put the alternator cable on the bottom right post and put the main fuse box wire over that one (with a brass nut separating the two) since that's how my truck was from the factory.

Cable 25862351 replaces the factory cable for a non TP2 truck and has a straight connector rather than the factory cable's 90 degree connector. It also has a second battery cable that connects to 19116352. It's the cable that runs along the top of the firewall and comes with metal mounting brackets. You'll need four speed nuts to connect it although you can do like I did and reuse the plastic connectors from the factory cable. I'll get speed nuts later.

Cable 25876897 is the aux battery negative cable that grounds directly to the engine block. It has a second wire that connects to the post on the right in the under hood junction box. I connected the charging wire for the trailer tow hitch to this post as well. If you do not have the TP2 option a 30 or 40 amp fuse must be added in order for the charging wire to work which causes the trailer charging wire to use the main battery. By connecting the aux battery cable and removing the fuse (or not adding one if you haven't previously connected the trailer tow wire) you isolate the charging wire to the aux battery while the truck is not running.

There is a plastic relay on cable 25862351 which has wires connected to the large relay (12135194) and a connection plug with three wires (red, orange and black). The plastic relay is used to activate relay 12135194 which is what isolates the aux battery from the charging system. I chose to use part 15305801 which is a four wire plastic connector that plugs into the relay connector. I did this because I could easily disconnect the connector which cuts the aux battery off from the charging system. In retrospect, I probably would not use it, though, since I can easily disconnect it at the relay (12135194) itself. If you use the four wire connector (15305801), though, it has four white/grey wires. You'll need to match up the wire colors to the relay and remove the fourth wire. I cut the wire loom on 25862351 and ran three wires next to the battery cable to the fuse box. On the X2 connector of the under hood junction box, using terminal connectors (13525970), the red wire goes to A5 and the orange wire goes to B4. The black wire goes to ground on the vehicle. I grounded it directly to the engine block where I grounded cable 25876897. I chose one of the threaded holes on the engine block near the alternator bracket for the ground using a 10x1.25 bolt.

Relay 12135194 must be mounted to the firewall of the truck. Non TP2 trucks do not have studs from the factory to mount this relay. I used self tapping screws to attach it to the truck. From the factory, the relay mounts just above and left of the chassis ground on the firewall. This is near the grounding strap from the hood to the firewall which is left of the brake booster. Two of the brass nuts purchased connect the battery cables to the relay. The relay mounts with the plug on the top. The battery cable from the mega fuse holder goes to the bottom stud and the positive battery cable to the aux battery goes on the top stud. Make sure you have enough slack in the battery cable and relay plug before you mount the relay. You don't want to mount it only to find out the cables won't reach!

The aux battery positive and negative cables have threaded studs to connect accessories. Two of the nuts purchased (not the brass ones) connect to these studs. I chose to add my accessories directly to the battery using these studs. You could easily connect accessories to the right post on the under hood fuse box where the trailer charge wire connects.

I spent over $300 to do this not including the battery. I know I could have used the Wrangler product but I wanted a factory setup. Plus, the Wrangler sales rep never sent me a quote even after three phone calls requesting it. This installation uses all factory parts and looks factory. You can hear the relay "clunk" when you turn the key to run. The auxiliary battery is isolated until the key is in the run position. It remains isolated when the ignition is cranking as well so you don't have to worry about a fully drained aux battery hampering starting if it's extremely cold outside or your main battery isn't in fantastic shape. I can now use the trailer tow wire in the 7-way connector and a three port 12-volt cigarette adapter in the back of the truck where I can run a fan for my dog box and not worry about running down my starting battery.

I've attached two pictures (thanks to those who sent them!). The Factory Harness Photos are picture of a truck with TP2 option from the factory. The aux_battery.jpg is a schematic of the TP2 option.

Factory_Harness_Photos.pdf

Edited September 10, 2009 by parshal

brims · September 10, 2009

Nice writeup. Kind of pricey, but looking factory has it's advatages.

jerseymike68 · September 12, 2009

Thank You!

Bikinjohn · September 30, 2009

Thanks for the awesome write up. Is there any way you can post pics of your install? The pdf pic was ok but I'd like to see a little more detail for the aux neg battery cable hookup, etc.

txab · September 30, 2009

Great write up. Thanks for sharing

jscan · December 1, 2009

sent u a pm about this topic, hope u can help...thanks

Cable · February 4, 2010

I installed an auxiliary battery in my '09 Sierra 1500 and thought I'd pass along how I did it so that there's one place to find info for others wanting to do this. There is no aux battery kit for the GMT 900 as there is with the 800. I gathered most of the information off this site from a few posts and PM's with different people. So, thanks to everyone who provided me information and sent pictures. I will post pictures that people sent me, too.

Here are the parts. There have been a few posts here with the parts for the GMT 900 but those lists are incomplete. In addition to the parts below you'll need 7 - 10 feet (overkill but enough) of 18 gauge wire in three colors. I bought mine at Radio Shack for $7 and it had red, green and black.

25876897-CABLE;NEGATIVE AUX BAT

15942730-CABLE;POSITIVE AUX BAT

25862351-CABLE;POSITIVE AUX BAT RH

21021808-NUT - read below for specifics

11609411-NUT - read below for specifics

12135194-RELAY;AUX BAT

15881616-COVER;AUX BAT POS JUNCTION BLOCK

14005061-RETAINER;AUX BAT HOLDOWN

11509853-BOLT;AUX BAT HOLDOWN

19116352-mega fuse holder

15305801-[inline-To Battery Positive Cable Connector]; Aux ; Aux Camper Bat (TP2) ; 4-Way male black; may be listed as O2 sensor connector but it's the same generic connector

13525970-terminal connectors (for X2 connector of the under hood junction box, pins B4 and A5)

For the nuts, you'll use more than two of the brass nuts. These nuts are used to connect cables to the mega fuse holder and relay. You can take some from the factory fuse holder but I still ended up using six. I don't know which part number above is for the brass nuts so you'll need to ask the parts guy. The other two nuts are used on the battery cable posts to connect accessory wires.

Part 19116352 replaces the existing mega fuse holder near the passenger hood hinge. Verify that you have two fuses, 175 AMP for the cable to fuse box and 125 AMP for the aux battery relay cable. I reused the existing 175 AMP fuse. I put the aux battery cable on the second post on the right side with the 125 AMP fuse. I put the alternator cable on the bottom right post and put the main fuse box wire over that one (with a brass nut separating the two) since that's how my truck was from the factory.

Cable 25862351 replaces the factory cable for a non TP2 truck and has a straight connector rather than the factory cable's 90 degree connector. It also has a second battery cable that connects to 19116352. It's the cable that runs along the top of the firewall and comes with metal mounting brackets. You'll need four speed nuts to connect it although you can do like I did and reuse the plastic connectors from the factory cable. I'll get speed nuts later.

Cable 25876897 is the aux battery negative cable that grounds directly to the engine block. It has a second wire that connects to the post on the right in the under hood junction box. I connected the charging wire for the trailer tow hitch to this post as well. If you do not have the TP2 option a 30 or 40 amp fuse must be added in order for the charging wire to work which causes the trailer charging wire to use the main battery. By connecting the aux battery cable and removing the fuse (or not adding one if you haven't previously connected the trailer tow wire) you isolate the charging wire to the aux battery while the truck is not running.

There is a plastic relay on cable 25862351 which has wires connected to the large relay (12135194) and a connection plug with three wires (red, orange and black). The plastic relay is used to activate relay 12135194 which is what isolates the aux battery from the charging system. I chose to use part 15305801 which is a four wire plastic connector that plugs into the relay connector. I did this because I could easily disconnect the connector which cuts the aux battery off from the charging system. In retrospect, I probably would not use it, though, since I can easily disconnect it at the relay (12135194) itself. If you use the four wire connector (15305801), though, it has four white/grey wires. You'll need to match up the wire colors to the relay and remove the fourth wire. I cut the wire loom on 25862351 and ran three wires next to the battery cable to the fuse box. On the X2 connector of the under hood junction box, using terminal connectors (13525970), the red wire goes to A5 and the orange wire goes to B4. The black wire goes to ground on the vehicle. I grounded it directly to the engine block where I grounded cable 25876897. I chose one of the threaded holes on the engine block near the alternator bracket for the ground using a 10x1.25 bolt.

Relay 12135194 must be mounted to the firewall of the truck. Non TP2 trucks do not have studs from the factory to mount this relay. I used self tapping screws to attach it to the truck. From the factory, the relay mounts just above and left of the chassis ground on the firewall. This is near the grounding strap from the hood to the firewall which is left of the brake booster. Two of the brass nuts purchased connect the battery cables to the relay. The relay mounts with the plug on the top. The battery cable from the mega fuse holder goes to the bottom stud and the positive battery cable to the aux battery goes on the top stud. Make sure you have enough slack in the battery cable and relay plug before you mount the relay. You don't want to mount it only to find out the cables won't reach!

The aux battery positive and negative cables have threaded studs to connect accessories. Two of the nuts purchased (not the brass ones) connect to these studs. I chose to add my accessories directly to the battery using these studs. You could easily connect accessories to the right post on the under hood fuse box where the trailer charge wire connects.

I spent over $300 to do this not including the battery. I know I could have used the Wrangler product but I wanted a factory setup. Plus, the Wrangler sales rep never sent me a quote even after three phone calls requesting it. This installation uses all factory parts and looks factory. You can hear the relay "clunk" when you turn the key to run. The auxiliary battery is isolated until the key is in the run position. It remains isolated when the ignition is cranking as well so you don't have to worry about a fully drained aux battery hampering starting if it's extremely cold outside or your main battery isn't in fantastic shape. I can now use the trailer tow wire in the 7-way connector and a three port 12-volt cigarette adapter in the back of the truck where I can run a fan for my dog box and not worry about running down my starting battery.

I've attached two pictures (thanks to those who sent them!). The Factory Harness Photos are picture of a truck with TP2 option from the factory. The aux_battery.jpg is a schematic of the TP2 option.

Cable · February 4, 2010

I installed an auxiliary battery in my '09 Sierra 1500 and thought I'd pass along how I did it so that there's one place to find info for others wanting to do this. There is no aux battery kit for the GMT 900 as there is with the 800. I gathered most of the information off this site from a few posts and PM's with different people. So, thanks to everyone who provided me information and sent pictures. I will post pictures that people sent me, too.

Here are the parts. There have been a few posts here with the parts for the GMT 900 but those lists are incomplete. In addition to the parts below you'll need 7 - 10 feet (overkill but enough) of 18 gauge wire in three colors. I bought mine at Radio Shack for $7 and it had red, green and black.

25876897-CABLE;NEGATIVE AUX BAT

15942730-CABLE;POSITIVE AUX BAT

25862351-CABLE;POSITIVE AUX BAT RH

21021808-NUT - read below for specifics

11609411-NUT - read below for specifics

12135194-RELAY;AUX BAT

15881616-COVER;AUX BAT POS JUNCTION BLOCK

14005061-RETAINER;AUX BAT HOLDOWN

11509853-BOLT;AUX BAT HOLDOWN

19116352-mega fuse holder

15305801-[inline-To Battery Positive Cable Connector]; Aux ; Aux Camper Bat (TP2) ; 4-Way male black; may be listed as O2 sensor connector but it's the same generic connector

13525970-terminal connectors (for X2 connector of the under hood junction box, pins B4 and A5)

For the nuts, you'll use more than two of the brass nuts. These nuts are used to connect cables to the mega fuse holder and relay. You can take some from the factory fuse holder but I still ended up using six. I don't know which part number above is for the brass nuts so you'll need to ask the parts guy. The other two nuts are used on the battery cable posts to connect accessory wires.

Part 19116352 replaces the existing mega fuse holder near the passenger hood hinge. Verify that you have two fuses, 175 AMP for the cable to fuse box and 125 AMP for the aux battery relay cable. I reused the existing 175 AMP fuse. I put the aux battery cable on the second post on the right side with the 125 AMP fuse. I put the alternator cable on the bottom right post and put the main fuse box wire over that one (with a brass nut separating the two) since that's how my truck was from the factory.

Cable 25862351 replaces the factory cable for a non TP2 truck and has a straight connector rather than the factory cable's 90 degree connector. It also has a second battery cable that connects to 19116352. It's the cable that runs along the top of the firewall and comes with metal mounting brackets. You'll need four speed nuts to connect it although you can do like I did and reuse the plastic connectors from the factory cable. I'll get speed nuts later.

Cable 25876897 is the aux battery negative cable that grounds directly to the engine block. It has a second wire that connects to the post on the right in the under hood junction box. I connected the charging wire for the trailer tow hitch to this post as well. If you do not have the TP2 option a 30 or 40 amp fuse must be added in order for the charging wire to work which causes the trailer charging wire to use the main battery. By connecting the aux battery cable and removing the fuse (or not adding one if you haven't previously connected the trailer tow wire) you isolate the charging wire to the aux battery while the truck is not running.

There is a plastic relay on cable 25862351 which has wires connected to the large relay (12135194) and a connection plug with three wires (red, orange and black). The plastic relay is used to activate relay 12135194 which is what isolates the aux battery from the charging system. I chose to use part 15305801 which is a four wire plastic connector that plugs into the relay connector. I did this because I could easily disconnect the connector which cuts the aux battery off from the charging system. In retrospect, I probably would not use it, though, since I can easily disconnect it at the relay (12135194) itself. If you use the four wire connector (15305801), though, it has four white/grey wires. You'll need to match up the wire colors to the relay and remove the fourth wire. I cut the wire loom on 25862351 and ran three wires next to the battery cable to the fuse box. On the X2 connector of the under hood junction box, using terminal connectors (13525970), the red wire goes to A5 and the orange wire goes to B4. The black wire goes to ground on the vehicle. I grounded it directly to the engine block where I grounded cable 25876897. I chose one of the threaded holes on the engine block near the alternator bracket for the ground using a 10x1.25 bolt.

Relay 12135194 must be mounted to the firewall of the truck. Non TP2 trucks do not have studs from the factory to mount this relay. I used self tapping screws to attach it to the truck. From the factory, the relay mounts just above and left of the chassis ground on the firewall. This is near the grounding strap from the hood to the firewall which is left of the brake booster. Two of the brass nuts purchased connect the battery cables to the relay. The relay mounts with the plug on the top. The battery cable from the mega fuse holder goes to the bottom stud and the positive battery cable to the aux battery goes on the top stud. Make sure you have enough slack in the battery cable and relay plug before you mount the relay. You don't want to mount it only to find out the cables won't reach!

The aux battery positive and negative cables have threaded studs to connect accessories. Two of the nuts purchased (not the brass ones) connect to these studs. I chose to add my accessories directly to the battery using these studs. You could easily connect accessories to the right post on the under hood fuse box where the trailer charge wire connects.

I spent over $300 to do this not including the battery. I know I could have used the Wrangler product but I wanted a factory setup. Plus, the Wrangler sales rep never sent me a quote even after three phone calls requesting it. This installation uses all factory parts and looks factory. You can hear the relay "clunk" when you turn the key to run. The auxiliary battery is isolated until the key is in the run position. It remains isolated when the ignition is cranking as well so you don't have to worry about a fully drained aux battery hampering starting if it's extremely cold outside or your main battery isn't in fantastic shape. I can now use the trailer tow wire in the 7-way connector and a three port 12-volt cigarette adapter in the back of the truck where I can run a fan for my dog box and not worry about running down my starting battery.

I've attached two pictures (thanks to those who sent them!). The Factory Harness Photos are picture of a truck with TP2 option from the factory. The aux_battery.jpg is a schematic of the TP2 option.

Thanks a bunch for this post. It is the most comprehensive collection of data I have found. I am having trouble finding the PN 13525970 terminal connectors for X2 connector. And I haven't been able to locate detailed instructions to add the connectors to X2, beyond disconnecting the batter, remove the cover, release the retainers securing the "underhood electrical center". Does the junction block bracket need to come off? How is X2 accessed for installing the two connectors?

jscan · February 9, 2010

I installed an auxiliary battery in my '09 Sierra 1500 and thought I'd pass along how I did it so that there's one place to find info for others wanting to do this. There is no aux battery kit for the GMT 900 as there is with the 800. I gathered most of the information off this site from a few posts and PM's with different people. So, thanks to everyone who provided me information and sent pictures. I will post pictures that people sent me, too.

Here are the parts. There have been a few posts here with the parts for the GMT 900 but those lists are incomplete. In addition to the parts below you'll need 7 - 10 feet (overkill but enough) of 18 gauge wire in three colors. I bought mine at Radio Shack for $7 and it had red, green and black.

25876897-CABLE;NEGATIVE AUX BAT

15942730-CABLE;POSITIVE AUX BAT

25862351-CABLE;POSITIVE AUX BAT RH

21021808-NUT - read below for specifics

11609411-NUT - read below for specifics

12135194-RELAY;AUX BAT

15881616-COVER;AUX BAT POS JUNCTION BLOCK

14005061-RETAINER;AUX BAT HOLDOWN

11509853-BOLT;AUX BAT HOLDOWN

19116352-mega fuse holder

15305801-[inline-To Battery Positive Cable Connector]; Aux ; Aux Camper Bat (TP2) ; 4-Way male black; may be listed as O2 sensor connector but it's the same generic connector

13525970-terminal connectors (for X2 connector of the under hood junction box, pins B4 and A5)

For the nuts, you'll use more than two of the brass nuts. These nuts are used to connect cables to the mega fuse holder and relay. You can take some from the factory fuse holder but I still ended up using six. I don't know which part number above is for the brass nuts so you'll need to ask the parts guy. The other two nuts are used on the battery cable posts to connect accessory wires.

Part 19116352 replaces the existing mega fuse holder near the passenger hood hinge. Verify that you have two fuses, 175 AMP for the cable to fuse box and 125 AMP for the aux battery relay cable. I reused the existing 175 AMP fuse. I put the aux battery cable on the second post on the right side with the 125 AMP fuse. I put the alternator cable on the bottom right post and put the main fuse box wire over that one (with a brass nut separating the two) since that's how my truck was from the factory.

Cable 25862351 replaces the factory cable for a non TP2 truck and has a straight connector rather than the factory cable's 90 degree connector. It also has a second battery cable that connects to 19116352. It's the cable that runs along the top of the firewall and comes with metal mounting brackets. You'll need four speed nuts to connect it although you can do like I did and reuse the plastic connectors from the factory cable. I'll get speed nuts later.

Cable 25876897 is the aux battery negative cable that grounds directly to the engine block. It has a second wire that connects to the post on the right in the under hood junction box. I connected the charging wire for the trailer tow hitch to this post as well. If you do not have the TP2 option a 30 or 40 amp fuse must be added in order for the charging wire to work which causes the trailer charging wire to use the main battery. By connecting the aux battery cable and removing the fuse (or not adding one if you haven't previously connected the trailer tow wire) you isolate the charging wire to the aux battery while the truck is not running.

There is a plastic relay on cable 25862351 which has wires connected to the large relay (12135194) and a connection plug with three wires (red, orange and black). The plastic relay is used to activate relay 12135194 which is what isolates the aux battery from the charging system. I chose to use part 15305801 which is a four wire plastic connector that plugs into the relay connector. I did this because I could easily disconnect the connector which cuts the aux battery off from the charging system. In retrospect, I probably would not use it, though, since I can easily disconnect it at the relay (12135194) itself. If you use the four wire connector (15305801), though, it has four white/grey wires. You'll need to match up the wire colors to the relay and remove the fourth wire. I cut the wire loom on 25862351 and ran three wires next to the battery cable to the fuse box. On the X2 connector of the under hood junction box, using terminal connectors (13525970), the red wire goes to A5 and the orange wire goes to B4. The black wire goes to ground on the vehicle. I grounded it directly to the engine block where I grounded cable 25876897. I chose one of the threaded holes on the engine block near the alternator bracket for the ground using a 10x1.25 bolt.

Relay 12135194 must be mounted to the firewall of the truck. Non TP2 trucks do not have studs from the factory to mount this relay. I used self tapping screws to attach it to the truck. From the factory, the relay mounts just above and left of the chassis ground on the firewall. This is near the grounding strap from the hood to the firewall which is left of the brake booster. Two of the brass nuts purchased connect the battery cables to the relay. The relay mounts with the plug on the top. The battery cable from the mega fuse holder goes to the bottom stud and the positive battery cable to the aux battery goes on the top stud. Make sure you have enough slack in the battery cable and relay plug before you mount the relay. You don't want to mount it only to find out the cables won't reach!

The aux battery positive and negative cables have threaded studs to connect accessories. Two of the nuts purchased (not the brass ones) connect to these studs. I chose to add my accessories directly to the battery using these studs. You could easily connect accessories to the right post on the under hood fuse box where the trailer charge wire connects.

I spent over $300 to do this not including the battery. I know I could have used the Wrangler product but I wanted a factory setup. Plus, the Wrangler sales rep never sent me a quote even after three phone calls requesting it. This installation uses all factory parts and looks factory. You can hear the relay "clunk" when you turn the key to run. The auxiliary battery is isolated until the key is in the run position. It remains isolated when the ignition is cranking as well so you don't have to worry about a fully drained aux battery hampering starting if it's extremely cold outside or your main battery isn't in fantastic shape. I can now use the trailer tow wire in the 7-way connector and a three port 12-volt cigarette adapter in the back of the truck where I can run a fan for my dog box and not worry about running down my starting battery.

I've attached two pictures (thanks to those who sent them!). The Factory Harness Photos are picture of a truck with TP2 option from the factory. The aux_battery.jpg is a schematic of the TP2 option.

does this setup run everything from both batt. when truck is running or is the 2nd batt. just used for accessories connected directly to it. i have a plow and i want to know if this setup will help me. doesnt sound like it, maybe thats why the plow prep pkg. doesnt come with a 2nd batt. but comes with a 160 amp alt.

parshal · February 25, 2010

does this setup run everything from both batt. when truck is running or is the 2nd batt. just used for accessories connected directly to it. i have a plow and i want to know if this setup will help me. doesnt sound like it, maybe thats why the plow prep pkg. doesnt come with a 2nd batt. but comes with a 160 amp alt.

I hadn't received notification of any of these posts so I'm sorry for the late responses.

When the key is on both batteries are in use. When the key is in the start or off position the two batteries are isolated. When the batteries are isolated, the auxiliary battery is not charging and anything connected to it will be using only it and not the starting battery.

parshal · February 25, 2010

Thanks a bunch for this post. It is the most comprehensive collection of data I have found. I am having trouble finding the PN 13525970 terminal connectors for X2 connector. And I haven't been able to locate detailed instructions to add the connectors to X2, beyond disconnecting the batter, remove the cover, release the retainers securing the "underhood electrical center". Does the junction block bracket need to come off? How is X2 accessed for installing the two connectors?

I have a mechanic friend who works at a Chevy dealer get the terminal connectors for me. He said that the parts person might have trouble finding it but that a mechanic would know how to get it from the parts desk. Again, my buddy soldered the X2 connector but (I'm doing this from memory here) you do remove the top of the electrical center by pulling the two plastic handles on each side up and work it loose. It's a little tough to get things lined up at first so don't force it. I'm not sure what the "junction block bracket" is. You have to locate the connector where you want to install the wires and pull that connector from the electrical center once the top is off. Basically, you need a special crimping tool to connect the wire to the connector to make it solid but I think you could do it with pliers if you were going to solder it. Once the connectors are on the wire you just push them into the connector and connect it back to the electrical center.

I'm sure that didn't answer your question very well. You can send me a PM and give you my phone number to call if you want a better explanation. You can email at the email address below as well since it doesn't seem like I'm getting post notifications. This email will only work for a short time. <[email protected]>

Cable · March 3, 2010

I installed an auxiliary battery in my '09 Sierra 1500 and thought I'd pass along how I did it so that there's one place to find info for others wanting to do this. There is no aux battery kit for the GMT 900 as there is with the 800. I gathered most of the information off this site from a few posts and PM's with different people. So, thanks to everyone who provided me information and sent pictures. I will post pictures that people sent me, too.

Here are the parts. There have been a few posts here with the parts for the GMT 900 but those lists are incomplete. In addition to the parts below you'll need 7 - 10 feet (overkill but enough) of 18 gauge wire in three colors. I bought mine at Radio Shack for $7 and it had red, green and black.

25876897-CABLE;NEGATIVE AUX BAT

15942730-CABLE;POSITIVE AUX BAT

25862351-CABLE;POSITIVE AUX BAT RH

21021808-NUT - read below for specifics

11609411-NUT - read below for specifics

12135194-RELAY;AUX BAT

15881616-COVER;AUX BAT POS JUNCTION BLOCK

14005061-RETAINER;AUX BAT HOLDOWN

11509853-BOLT;AUX BAT HOLDOWN

19116352-mega fuse holder

15305801-[inline-To Battery Positive Cable Connector]; Aux ; Aux Camper Bat (TP2) ; 4-Way male black; may be listed as O2 sensor connector but it's the same generic connector

13525970-terminal connectors (for X2 connector of the under hood junction box, pins B4 and A5)

For the nuts, you'll use more than two of the brass nuts. These nuts are used to connect cables to the mega fuse holder and relay. You can take some from the factory fuse holder but I still ended up using six. I don't know which part number above is for the brass nuts so you'll need to ask the parts guy. The other two nuts are used on the battery cable posts to connect accessory wires.

Part 19116352 replaces the existing mega fuse holder near the passenger hood hinge. Verify that you have two fuses, 175 AMP for the cable to fuse box and 125 AMP for the aux battery relay cable. I reused the existing 175 AMP fuse. I put the aux battery cable on the second post on the right side with the 125 AMP fuse. I put the alternator cable on the bottom right post and put the main fuse box wire over that one (with a brass nut separating the two) since that's how my truck was from the factory.

Cable 25862351 replaces the factory cable for a non TP2 truck and has a straight connector rather than the factory cable's 90 degree connector. It also has a second battery cable that connects to 19116352. It's the cable that runs along the top of the firewall and comes with metal mounting brackets. You'll need four speed nuts to connect it although you can do like I did and reuse the plastic connectors from the factory cable. I'll get speed nuts later.

Cable 25876897 is the aux battery negative cable that grounds directly to the engine block. It has a second wire that connects to the post on the right in the under hood junction box. I connected the charging wire for the trailer tow hitch to this post as well. If you do not have the TP2 option a 30 or 40 amp fuse must be added in order for the charging wire to work which causes the trailer charging wire to use the main battery. By connecting the aux battery cable and removing the fuse (or not adding one if you haven't previously connected the trailer tow wire) you isolate the charging wire to the aux battery while the truck is not running.

There is a plastic relay on cable 25862351 which has wires connected to the large relay (12135194) and a connection plug with three wires (red, orange and black). The plastic relay is used to activate relay 12135194 which is what isolates the aux battery from the charging system. I chose to use part 15305801 which is a four wire plastic connector that plugs into the relay connector. I did this because I could easily disconnect the connector which cuts the aux battery off from the charging system. In retrospect, I probably would not use it, though, since I can easily disconnect it at the relay (12135194) itself. If you use the four wire connector (15305801), though, it has four white/grey wires. You'll need to match up the wire colors to the relay and remove the fourth wire. I cut the wire loom on 25862351 and ran three wires next to the battery cable to the fuse box. On the X2 connector of the under hood junction box, using terminal connectors (13525970), the red wire goes to A5 and the orange wire goes to B4. The black wire goes to ground on the vehicle. I grounded it directly to the engine block where I grounded cable 25876897. I chose one of the threaded holes on the engine block near the alternator bracket for the ground using a 10x1.25 bolt.

Relay 12135194 must be mounted to the firewall of the truck. Non TP2 trucks do not have studs from the factory to mount this relay. I used self tapping screws to attach it to the truck. From the factory, the relay mounts just above and left of the chassis ground on the firewall. This is near the grounding strap from the hood to the firewall which is left of the brake booster. Two of the brass nuts purchased connect the battery cables to the relay. The relay mounts with the plug on the top. The battery cable from the mega fuse holder goes to the bottom stud and the positive battery cable to the aux battery goes on the top stud. Make sure you have enough slack in the battery cable and relay plug before you mount the relay. You don't want to mount it only to find out the cables won't reach!

The aux battery positive and negative cables have threaded studs to connect accessories. Two of the nuts purchased (not the brass ones) connect to these studs. I chose to add my accessories directly to the battery using these studs. You could easily connect accessories to the right post on the under hood fuse box where the trailer charge wire connects.

I spent over $300 to do this not including the battery. I know I could have used the Wrangler product but I wanted a factory setup. Plus, the Wrangler sales rep never sent me a quote even after three phone calls requesting it. This installation uses all factory parts and looks factory. You can hear the relay "clunk" when you turn the key to run. The auxiliary battery is isolated until the key is in the run position. It remains isolated when the ignition is cranking as well so you don't have to worry about a fully drained aux battery hampering starting if it's extremely cold outside or your main battery isn't in fantastic shape. I can now use the trailer tow wire in the 7-way connector and a three port 12-volt cigarette adapter in the back of the truck where I can run a fan for my dog box and not worry about running down my starting battery.

I've attached two pictures (thanks to those who sent them!). The Factory Harness Photos are picture of a truck with TP2 option from the factory. The aux_battery.jpg is a schematic of the TP2 option.

Cable · March 3, 2010

My 2008 Silverado 2500 had the X122 connector prewired and located below the right side battery between the battery and the air condition accumulator. If your job requires installing the connector you need to know that the same connector is used on GM 4.3 liter oxygen sensors. Ask a shop to save you an old sensor.

The 125 amp mega fuse has a GM PN of 12177251.

The required ground bolt was a 10X1.5-20 as opposed to the 10X1.25 used on the author's truck.

There is a fusible link on the auxiliary battery cable but it was too short to make it to the underhood fuse box stud. I cut it off the cable, taped the stub, and added a crimped and soldered ring terminal to the bare end. Terminals on fusible links not only need to be crimped but soldered too.

Battery cable connector for the underhood fuse box, X6 has two release tabs. After releasing the two tabs the connector is rotated up from the cable end. Be careful not to break the tabs.

Edited March 4, 2010 by Cable

Cable · March 4, 2010

Battery cable connector for the underhood fuse box, X6 has two release tabs. After releasing the two tabs the connector is rotated up from the cable end. Be careful not to break the tabs.

Cable · March 4, 2010

There is a fusible link on the auxiliary battery cable but it was too short to make it to the underhood fuse box stud. I cut it off the cable, taped the stub, and added a crimped and soldered ring terminal to the bare end. Terminals on fusible links not only need to be crimped but soldered too.