AUX switch install

Sserzan · October 31, 2017

I guess I am one of the lucky ones. I went to install the switch today on my ‘15 Silverado 1500 LS. My truck already had wiring for the AUX locations in the connector. I’m assuming GM uses the same harness for the WT and the LS as they are both lower end trucks. I’m having a friend that works at a dealer see if he can find the wiring diagrams for the harness. So I can install the relays and fuses and pull power from the relay. Has anyone else run into this?

Jmiller11331 · October 31, 2017

For most of you you don't want to put holes in your new truck. I have a solution for you. If you haven't seen it already.

On some of these trucks (ie work models) you can get upfitter switches that go where your traction control and cargo light switches go.

Trucks with only "traction control" & "cargo lights" can use this. ( if your truck has bed lights or a park assist it won't work.)

Looks like this the empty switch is just a blank. (Does nothing)
This switches are ground controlling. So you can hook them up to the negative of a relay. Mine are on the way and I'll take/show how it works.

I have factory bed lights that tie into the cargo light, so does that mean this won't work?

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smcgillis10 · October 31, 2017

I don't think your bed lights would cause any issues. Pretty sure they are wired in after the switches. Should be fine.

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WesternMike · November 1, 2017

Is there a way I can tell if I have wiring and fuses in place for this? I have the 2014 1500 WT2

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desertz · November 1, 2017

Is there a way I can tell if I have wiring and fuses in place for this? I have the 2014 1500 WT2

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Yes. You can tell by RPO code and by how your underhood fuse box is set up.

Go to www.gmupfitter.com and look through the technical bulletins for your vehicle.

But I believe if you were set up for this you'd already have the switch installed.

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aseibel · November 1, 2017

8 hours ago, mikevickers10 said:

Is there a way I can tell if I have wiring and fuses in place for this? I have the 2014 1500 WT2

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The main thing to look at is your main fuse panel under the hood. You probably have a bunch of blank spots in there. Check the numbers and look for those aux switches.

Even if you have a wiring harness to the switches, they won't do anything if there is no fuse/relay on the back end. I was hoping I could install it in my LT, but my fuse box is missing those items.

tha_lildude · November 3, 2017

I have just successfully fully integrated my AUX switches OEM style. My fuse block did not come with the relays or fuses, nor did it have connectors for them. I had to purchase a few new things.

Underhood Fuse Block - Part #84075778 Price $208.50
Aux switches - Part #23145158 Price $73.21
Wire - Part #13578892 Price $9.93 Qty. 4
Wire - Part #13575832 Price $9.93 Qty. 8

Yes I know this was expensive but it is now pretty much completely OEM.

I did have the wiring that came out of the back of the original switch. The four wires that correspond with the aux switches are

Red/White - Aux 1
Yellow/White - Aux 2
Green/Gray - Aux 3
White/Blue - Aux 4 (I forgot which color this was but on a diagram I have it says WH/BU)

The wires run down to the big junction box near the floor and brake pedal. They run into there but they do not come out the back. They run into the bottom right connector and there is continuity to terminals on the back. You will need to test them. Get your continuity tester, one lead goes on the front and the other, start touching all of them on the back. You then get *Wire and insert it into the junction connector that corresponds to the continuity you tested for. I used a different color tape on each wire as I plugged them in so I knew which was aux 1, 2, 3, and 4. You will need to pull up the top little plastic piece on the junction connector to insert the wire.

The new *Underhood Fuse Block changes in reference to the one my truck came with were four auxiliary fuses and relays, and a second fuel pump fuse. Here is where it is a little tricky but I will do my best to explain. You will need to remove your fuse block. On the underside you will see a few pins are different. On one of the connectors, it will be different due to the second fuel pump connector (no wire is ran to it though). The two others ones that are different are the middle one toward the firewall side of the truck, and the firewall driver fender side. Those are the only two you need to get into. Pull the junction connector up (there is a tab that you push, you then slide the connector toward the firewall about a 1/2" then it'll lift out) Undo the tape, cut the zip tie (if necessary, but replace it) and then pull off the underside cover to access the holes to insert the pins from the *Wire. I can't explain how to get it off but if you got this far, you will figure it out and don't break it, its easy to come off once you figure it out.

Back to the Fuse block. **Pay attention or you will wire it wrong** What I did was slightly lift the relays and you will need to test each of the four leads for continuity. One will have continuity to the fat spade (This one feeds hot to the whole junction connector) and this corresponds to 30. You will find two medium spades that correspond to 87 and to 85. You will find a small spade corresponds to 86. You will plug in your big *Wire to the medium spade that corresponds to 87 that is ALSO different then the original fuse block. Your new fuse block will have the spade, your old fuse block will not have the spade. If this is true, this is the one you will insert the medium *Wire into the junction connector. You do this for all four relays. You also need to test continuity for 86 and a small spade and again, your new fuse block will have the small spade, your old one will not. There are two small spades and one big spade in the junction connector closest to the fender and firewall. The rest go in the middle toward the firewall.

Now you have all of your connections made, you need to connect the small *Wires together. Make sure you mark the wires (I used different colored tape) that correspond to the relay that activates aux1, 2, 3, and 4. I also put a little tape on each relay so I wouldn't forget which tape meant what. I soldered on a roughly 16" piece of wire to the small *Wire and punched it through the rubber grommet that is on the firewall. There is a little nipple looking piece that sticks out, I cut a small X and pushed the wires in. Attach those to the wires you plugged in inside the truck in the junction connector.

Now all you have to do is install your switch and plug your lightbar, caution light, backup light, or whatever it is you want to the big *Wire and it will provide power to it.

I hope this helps someone.

The dealer, two of them face to face, and two of them that I called mentioned it couldn't be done OEM. I do car electrical daily so I knew better. One explained the BCM will throw codes especially if the truck doesn't have plow prep blah blah blah. None of this runs through any voltage monitoring. That's all nonsense and was their excuse for being lazy. Document 110L states it can't be done as well. It can, it's just expensive.

chrispassas21 · November 4, 2017

I have just successfully fully integrated my AUX switches OEM style. My fuse block did not come with the relays or fuses, nor did it have connectors for them. I had to purchase a few new things.
Underhood Fuse Block - Part #84075778    Price $208.50

Aux switches - Part #23145158   Price $73.21

Wire - Part #13578892  Price $9.93 Qty. 4

Wire - Part #13575832 Price $9.93 Qty. 8
Yes I know this was expensive but it is now pretty much completely OEM.
I did have the wiring that came out of the back of the original switch. The four wires that correspond with the aux switches are
Red/White - Aux 1

Yellow/White - Aux 2

Green/Gray - Aux 3

White/Blue - Aux 4 (I forgot which color this was but on a diagram I have it says WH/BU)
The wires run down to the big junction box near the floor and brake pedal. They run into there but they do not come out the back. They run into the bottom right connector and there is continuity to terminals on the back. You will need to test them. Get your continuity tester, one lead goes on the front and the other, start touching all of them on the back. You then get *Wire and insert it into the junction connector that corresponds to the continuity you tested for. I used a different color tape on each wire as I plugged them in so I knew which was aux 1, 2, 3, and 4. You will need to pull up the top little plastic piece on the junction connector to insert the wire.

The new *Underhood Fuse Block changes in reference to the one my truck came with were four auxiliary fuses and relays, and a second fuel pump fuse. Here is where it is a little tricky but I will do my best to explain. You will need to remove your fuse block. On the underside you will see a few pins are different. On one of the connectors, it will be different due to the second fuel pump connector (no wire is ran to it though). The two others ones that are different are the middle one toward the firewall side of the truck, and the firewall driver fender side. Those are the only two you need to get into. Pull the junction connector up (there is a tab that you push, you then slide the connector toward the firewall about a 1/2" then it'll lift out) Undo the tape, cut the zip tie (if necessary, but replace it) and then pull off the underside cover to access the holes to insert the pins from the *Wire. I can't explain how to get it off but if you got this far, you will figure it out and don't break it, its easy to come off once you figure it out.

Back to the Fuse block. **Pay attention or you will wire it wrong** What I did was slightly lift the relays and you will need to test each of the four leads for continuity. One will have continuity to the fat spade (This one feeds hot to the whole junction connector) and this corresponds to 30. You will find two medium spades that correspond to 87 and to 85. You will find a small spade corresponds to 86. You will plug in your big *Wire to the medium spade that corresponds to 87 that is ALSO different then the original fuse block. Your new fuse block will have the spade, your old fuse block will not have the spade. If this is true, this is the one you will insert the medium *Wire into the junction connector. You do this for all four relays. You also need to test continuity for 86 and a small spade and again, your new fuse block will have the small spade, your old one will not. There are two small spades and one big spade in the junction connector closest to the fender and firewall. The rest go in the middle toward the firewall.

Now you have all of your connections made, you need to connect the small *Wires together. Make sure you mark the wires (I used different colored tape) that correspond to the relay that activates aux1, 2, 3, and 4. I also put a little tape on each relay so I wouldn't forget which tape meant what. I soldered on a roughly 16" piece of wire to the small *Wire and punched it through the rubber grommet that is on the firewall. There is a little nipple looking piece that sticks out, I cut a small X and pushed the wires in. Attach those to the wires you plugged in inside the truck in the junction connector.

Now all you have to do is install your switch and plug your lightbar, caution light, backup light, or whatever it is you want to the big *Wire and it will provide power to it.

I hope this helps someone.

The dealer, two of them face to face, and two of them that I called mentioned it couldn't be done OEM. I do car electrical daily so I knew better. One explained the BCM will throw codes especially if the truck doesn't have plow prep blah blah blah. None of this runs through any voltage monitoring. That's all nonsense and was their excuse for being lazy. Document 110L states it can't be done as well. It can, it's just expensive.

This is awesome! Have any kind of pictures???

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tha_lildude · November 4, 2017

52 minutes ago, chrispassas21 said:

This is awesome! Have any kind of pictures???

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I will get some and put them up soon.

tha_lildude · November 5, 2017

Inside driver junction connector by brake pedal. Bottom right connector. Be careful because there are multiple yellow/white and white/blue. I don't remember exactly if there are other multiples but test continuity from the wire to the wire behind the AUX switch. Then test continuity from front of junction box to rear of junction box.

tha_lildude · November 5, 2017

Rear of junction connector. This is where I inserted four of the small *Wire. I found continuity from front to back of junction connector. Remove three 10mm nuts to pull up junction box for better access. Note tape colors on wires, and one not color taped.

tha_lildude · November 5, 2017

Pictures of new and old Underhood fuse block. On the new block, red indicates trigger wire, or wire that will go from junction connector to red marks. Blue marks are the output power to whatever you want to be powered. Blue is big *Wire and red gets small *Wire. Do your due diligence and ensure they are correct! I do not remember 100% if these were the ones I used but I do believe I did. But again, test to ensure.

tha_lildude · November 5, 2017

Two fuse block tops compared. Relays circled. One is for a second fuel pump and the others are for aux. Fuses pertaining to aux are there but not identified. You can tell from comparing though.

Tomstruck · November 30, 2017

On 11/4/2017 at 11:52 PM, tha_lildude said:

Rear of junction connector. This is where I inserted four of the small *Wire. I found continuity from front to back of junction connector. Remove three 10mm nuts to pull up junction box for better access. Note tape colors on wires, and one not color taped.

Where did you have to run these wires too? did you just have to go to another connector that plugs into the fuse block under the hood?

tha_lildude · November 30, 2017

13 hours ago, Tomstruck said:

Where did you have to run these wires too? did you just have to go to another connector that plugs into the fuse block under the hood?

Yes. I had to extend them a bit but they ran through the firewall, into the fuse block and another small *wire was put into the connectors that the fuse block plugs into. There should be pictures of where the wires run into but I had taped it all back up before I took pictures so I cant say for sure exactly what pin number it is but if you look at the pictures you can see the small *wire run into the junction connector that the fuse block plugs into.