High beam and reverse light signal?

FirstAscent · May 8, 2020

Hey everyone,

I need to get a signal wire for my high beams and reverse lights, preferably from under the dash near the gas/brake pedals.

I already have a good signal wire for ACC power and parking lights which I also needed (thanks upfitter switches) but these are the last two signals I need to finish a project.

To be fair I haven’t looked too much yet, so reaching out to see if someone has already located either of these [emoji3526]

For the reverse lights I don’t want to go to the tail lights, I want to keep the wiring internal. I’m sure there’s one somewhere close to here.

Maybe one of you has wiring schematics? That’d be epic!

mkeddie · May 8, 2020

Won't be digging into this till next week or so but will let u know if u haven't found it yet

Are u looking for relay activation wire or power to lights

Sent from my Moto Z (2) using Tapatalk

FirstAscent · May 8, 2020

Won't be digging into this till next week or so but will let u know if u haven't found it yet

Sent from my Moto Z (2) using Tapatalk

Thanks! I’ll post up if/when I find something as well.

FirstAscent · May 9, 2020

Well that was much easier to figure out than I expected! Well done GM!

If you lookup your vehicle on the main gm upfitter website you can download some great material, including wiring schematics.

Tons of good info in here, I’ve got full pinout descriptions from the BCM (body control module) to get the signals I need.

I’m gonna take acc power from my upfitter harness but I’m posting up acc ignition power from the bcm in case anyone needs it that doesn’t have upfitters.

If anyone has any questions or needs help finding something for your specific needs I’d be happy to help, just ask. The wiring schematic is pretty clear though but I know that stuff can be confusing for some.

unit · May 9, 2020

Good post and very helpful. I'd like to find the wire from the BCM for the courtesy lights so that I can install footwell lights. I'd like them to come on when a door is opened and go out with the overhead lights. I looked at the GM Upfitter Home site but I didn't find the schematics. I would appreciate some help with this one!

FirstAscent · May 9, 2020

Good post and very helpful. I'd like to find the wire from the BCM for the courtesy lights so that I can install footwell lights. I'd like them to come on when a door is opened and go out with the overhead lights. I looked at the GM Upfitter Home site but I didn't find the schematics. I would appreciate some help with this one!

I “think” this is what you need. The hardest part, which isn’t hard, is determining the language, some things are obvious, others have a few options.

I highlighted Interior Lamp Control from x1 on the bcm, but there are some potential options on x2 as well.

Also, this is the direct link to the entire schematic file, BCM I’m referencing starts on page 379.

Important NOTE: the pinouts are reversed (mirror image) from what you see in the pdf if you were to be looking up at the bcm like the photo in my first post.. Think of it like this, if you were to unplug the plug and look at it head on, then it would be correct. I hope that makes sense. If it doesn’t then just trust me haha. But you can also just confirm the wire color to ensure you’re looking at the correct wire.

https://www.gmupfitter.com/files/media/photo/1291/20_Silverado_2500HD_3500HD_Electrical_Body_Builder_2019JUN21.pdf

unit · May 9, 2020

All I can say is thanks a bunch! That's exactly what I've been looking for. Super job!

FirstAscent · May 9, 2020

All I can say is thanks a bunch! That's exactly what I've been looking for. Super job!

Happy to help! Others have helped me plenty!
I see you have a Chevy from you’re avatar, as do I. The link I posted is for Chevy, I’ll post up the link for GMC when I get home for anyone else.

unit · May 9, 2020

OK, my next question is how do I identify the X2 module looking at the row of connectors in the BCM? I was hoping they would be marked but all I see are color tags.

FirstAscent · May 9, 2020

OK, my next question is how do I identify the X2 module looking at the row of connectors in the BCM? I was hoping they would be marked but all I see are color tags.

Simple! Once you realize the color reference [emoji3526]

See this photo, what I circled is the color of the plug, so this would be blue.

Also, it goes in order with x1 being the first plug, x2 being the second, and so on from left to right looking up at the bcm.

See my bcm photo in the first post, white (NA) is the first plug x1, blue (BU) is next X2, and so on.

Hope thy helps

Dunn · May 9, 2020

this is different but I saw a video of guy who linked a connector between 2 modules to activate reverse lights without having to push the button and seems pretty simple...this maybe useful for some peeps on here who tow trailers or in general

Edited May 9, 2020 by Dunn

Dunn · May 9, 2020

is there a way to make the tow mirrors auto fold when parking and shutting off the truck.....probably those same modules

unit · May 9, 2020

Thanks again FirstAscent. Makes sense now but I would never have guessed that NA means white. I think I can do it now. All the best!

FirstAscent · May 10, 2020

Instructions for looking up your specific vehicle

1. Go to https://www.gmupfitter.com
2. Click on Body Builder Manuals (protein brah!, haha)
3. Click on LIGHT Duty Vehicles (yes even for the 2500/3500)
4. Click on Light Duty 2020 (or whatever year you have/need)
5. Click Full Size C/K trucks/SUVs
6. Click on “Chevrolet Silverado/GMC Sierra Pick up and Chassis Cab Applications”
7. Select either Chevy or GMC 2500/3500 ELECTRICAL section
8. Have fun with your project!

is there a way to make the tow mirrors auto fold when parking and shutting off the truck.....probably those same modules

I’m surprised this isn’t a feature by default. Would be so easy for GM to simply add it via software update and let you choose it in the settings.

I don’t think it’d be too hard to do, would just need to find the right signal that enables/disabled already in that situation

I’d have to look at the voltage of the factory mirror fold button. I imagine it’s maybe momentary instead of 12v open, 0v closed.

Thanks again FirstAscent. Makes sense now but I would never have guessed that NA means white. I think I can do it now. All the best!

Happy to help! Let me know if you have any other questions.

Dunn · May 10, 2020

Yeah I know alot of vehicles do this automatically so was kinda surprised these didnt....I actually thought something was wrong when they didn't do it.....

But your right its just about sending the right signal I believe

That video I found about reverse lights was when I was searching for this feature