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
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.
Edited by parshal, 10 September 2009 - 12:54 PM.