GMC Sierra All-Terrain X 3rd brake light re-wire after removing stock

[kweable]

Has anyone taken off the roll bar of a All-Terrain X and re-wired the 3rd brake light???

 

Love the truck, didn't like the roll bar, want my 3rd brake light to work

Thanks!!!

Edited October 20, 2016 by kweable

[TxTruckMan]

I'm not familiar with the All-Terrain X specifically, but I researched this for my wife's Colorado. The addition of the roll bar for the Colorado Trail Boss is a dealer installed package and the bar is just plug and play into the truck harness. You unplug the harness for the 3rd brake light and connect the roll bar in it's place. The dealership let me talk to their prep guys who did the work. I would guess that it's a similar situation with these trucks. You might call your dealer and ask to speak with their prep guys.

[Crstfr]

truck is sick man!

[kweable]

truck is sick man!

Thank ya sir!!!

[kweable]

I'm not familiar with the All-Terrain X specifically, but I researched this for my wife's Colorado. The addition of the roll bar for the Colorado Trail Boss is a dealer installed package and the bar is just plug and play into the truck harness. You unplug the harness for the 3rd brake light and connect the roll bar in it's place. The dealership let me talk to their prep guys who did the work. I would guess that it's a similar situation with these trucks. You might call your dealer and ask to speak with their prep guys.

Appreciate your insight!!!

I did unplug the light that was wired to the roll bar. Now I have an empty plug underneath the truck which, in my mind, should plug up to the 3rd brake light on top of the cab. But...no one, including several different GMC dealerships, knows where the 3rd brake light plug is located and if it would even plug back up to the one that the roll bar was plugged into.

Funny thing is, the light works when you flip the switch on the dashboard but the brake light portion doesn't.

Thanks!!!

[jhplak325]

Is the bulb installed?

[Penguin VII]

No idea on the wiring but love your truck. I gotta say, I wasn't a fan of those roll bars in the back but the more I see them the more they grow on me.

 

Sent from my Nexus 6P using Tapatalk

[CobraCmdr]

Finally found a post about this!

Newbie here, I'm in the same boat as the OP

As I was taking out the sport bar, I had a feeling the third brake light wouldn't work, but was hoping a relay or something else would activate the cab brake light if it didn't detect the sport bar brake light (wishful thinking...LOL)

I tried changing bulbs on the cab brake light, even rotated the bulb (not sure if it matters)...nothing

I checked the CHMSL fuse to make sure it was good, or even there. It was there and good.

I noticed the wiring for the harness for the sport bar brake light was the same as the wiring for the harness on the cab brake light (at least the color coding was the same), so I decided to follow the sport bar harness wiring underneath to see where it led. It ended up at a junction where the factory had spliced into/onto the main wiring under the truck. Maybe the cab wiring is not connected here? I dunno.

At this point, I stopped tinkering. Didn't want to open anything up that might void warranties (truck's only a few months old LOL)

I made service appt with my dealer and am going to tell them what I've figured out so far...hoping it will help lead to a quick fix before I get pulled over by a quota happy cop! xD

I'll update here if the dealer finds a fix.

[kweable]

Finally found a post about this!

 

Newbie here, I'm in the same boat as the OP

 

As I was taking out the sport bar, I had a feeling the third brake light wouldn't work, but was hoping a relay or something else would activate the cab brake light if it didn't detect the sport bar brake light (wishful thinking...LOL)

 

I tried changing bulbs on the cab brake light, even rotated the bulb (not sure if it matters)...nothing

 

I checked the CHMSL fuse to make sure it was good, or even there. It was there and good.

 

I noticed the wiring for the harness for the sport bar brake light was the same as the wiring for the harness on the cab brake light (at least the color coding was the same), so I decided to follow the sport bar harness wiring underneath to see where it led. It ended up at a junction where the factory had spliced into/onto the main wiring under the truck. Maybe the cab wiring is not connected here? I dunno.

 

At this point, I stopped tinkering. Didn't want to open anything up that might void warranties (truck's only a few months old LOL)

 

I made service appt with my dealer and am going to tell them what I've figured out so far...hoping it will help lead to a quick fix before I get pulled over by a quota happy cop! xD

 

I'll update here if the dealer finds a fix.

 

Great info. Thanks for letting me know what all you have tried and please, if you don't mind, let me know what you find out from the dealer. Mine acted like they couldn't figure it out and that it wasn't their problem.

[newdude]

This may help you out:

 

Base CHMSL Front Harness Installation

1. This harness is used to provide CHMSL function to the Sport Bar if the vehicle does not also get Sport Bar mounted Off Road Lamps. If the vehicle also gets Sport Bar Lights, use the larger harness that comes with the Light Kit instead. Follow these instructions plus the additional instructions with the Light Kit for the larger harness.
2. The harness routing starts with the 3-way connector mounted to the inboard side of the UEC (1) (Underhood Electrical Center) with terminals pointing rearward.

Ground Installation

1. The ground eyelet will route forward and the two loose terminals will route rearward.
2. The ground is located on the front frame rail, near where a left tow hook would be located.
3. Remove the existing ground bolt (2), stack the new eyelet (1) and replace the ground bolt, tighten the bolt to 23 N.m (17 lb ft).
4. The two loose terminals route around the rear and into the UEC. The 1.5 mm terminal on the slightly shorter wire is for Sierra/Silverado and the 2.8 mm terminal on the slightly longer wire is for the Canyon/Colorado. The current CHMSL on the rear of the cab needs to be disabled, because the sport bar will block it from being viewed from behind. The new CHMSL in the sport bar will replace it.

UEC (Underhood Electrical Center)

1. Remove the top of the UEC (1), exposing the large connectors below.
2. Locate the CHMSL circuit in cavity M6 of UEC connector X3. It will be the grey, rear, outboard connector.
3. Remove the terminal from cavity M6. It will be a VT/GY wire. Replace it with the smaller of the two terminals, with the shorter wire length on the new accessory harness.
4. Cover the terminal that was removed and the un-needed terminal from the accessory harness with vinyl tape and store them out of the way.

5. Note: Do not cut off the terminal that was removed, the vehicle owner may want to return to the original CHMSL.

   Reassemble the UEC making sure it is fully seated before engaging the locking levers.

 

 

 

The key piece of info you need is this:

 

Cover the terminal that was removed and the un-needed terminal from the accessory harness with vinyl tape and store them out of the way.

Note: Do not cut off the terminal that was removed, the vehicle owner may want to return to the original CHMSL.

 

 

 

If you get the UBEC out, there should still be the terminals for the original CHMSL just taped/tied to something. All you'd have to do is remove the terminals that took their place for the sport bar, and put the old ones back in.

Edited November 14, 2016 by 15HDriver

[CobraCmdr]

Great info. Thanks for letting me know what all you have tried and please, if you don't mind, let me know what you find out from the dealer. Mine acted like they couldn't figure it out and that it wasn't their problem.

 

Will do! Apparently my dealer's service team has a great rep from the reviews I'm reading. I'll put 'em to the test with this one! LOL

 

I found out some more info thanks to 15HDriver's post, see below

 

 

This may help you out:

 

 

 

The key piece of info you need is this:

 

 

 

If you get the UBEC out, there should still be the terminals for the original CHMSL just taped/tied to something. All you'd have to do is remove the terminals that took their place for the sport bar, and put the old ones back in.

 

 

This info was perfect 15HDriver!

 

I had a hard time picturing where the harness would be in/near the UBEC, so thanks to some keywords from the info you posted, I was able to search online a bit more and found another post about this exact issue where a Silverado owner removed their sport bar and had the same problem: http://www.justanswer.com/chevy/9odun-chevrolet-silverado-1500-classic-lt-removed-factory.html

 

The tech's responses gave me even more keywords to search with and lo-and-behold I found a diagrammed installation for the sport bar on an eBay seller's storefront: http://www.ebay.com/itm/2016-GMC-Sierra-Bed-Mounted-Sport-Bar-23387669-Genuine-OEM-GM-/112026710099

 

About half way down the install diagram, the UEC is shown and they have a diagram of how to take it out and also where the harness should be.

 

I decided to take a stab at it and was able to get as far as removing the UEC part way and found what I think the factory harness to sport bar harness was. I just couldn't find the original terminal...or I wasn't reading the instructions right. I saw a similar connector deeper down in the bay, but I wasn't comfortable just pulling plugs all over the place LOL. I'd post pics, but it was getting dark out (don't really have a work area at my place where I can fit my truck atm LOL)

 

I think I might have missed this step:

• Locate the CHMSL circuit in cavity M6 of UEC connector X3. It will be the grey, rear, outboard connector.
• Remove the terminal from cavity M6. It will be a VT/GY wire. Replace it with the smaller of the two terminals, with the shorter wire length on the new accessory harness.

Anyways, I'm gonna try again tomorrow and will post pics of what I find. Worst comes to worst, I can explain in detail what I've tried and searched for to my dealer service crew

[kweable]

 

Will do! Apparently my dealer's service team has a great rep from the reviews I'm reading. I'll put 'em to the test with this one! LOL

 

I found out some more info thanks to 15HDriver's post, see below

 

 

This info was perfect 15HDriver!

 

I had a hard time picturing where the harness would be in/near the UBEC, so thanks to some keywords from the info you posted, I was able to search online a bit more and found another post about this exact issue where a Silverado owner removed their sport bar and had the same problem: http://www.justanswer.com/chevy/9odun-chevrolet-silverado-1500-classic-lt-removed-factory.html

 

The tech's responses gave me even more keywords to search with and lo-and-behold I found a diagrammed installation for the sport bar on an eBay seller's storefront: http://www.ebay.com/itm/2016-GMC-Sierra-Bed-Mounted-Sport-Bar-23387669-Genuine-OEM-GM-/112026710099

 

About half way down the install diagram, the UEC is shown and they have a diagram of how to take it out and also where the harness should be.

 

I decided to take a stab at it and was able to get as far as removing the UEC part way and found what I think the factory harness to sport bar harness was. I just couldn't find the original terminal...or I wasn't reading the instructions right. I saw a similar connector deeper down in the bay, but I wasn't comfortable just pulling plugs all over the place LOL. I'd post pics, but it was getting dark out (don't really have a work area at my place where I can fit my truck atm LOL)

 

I think I might have missed this step:

• Locate the CHMSL circuit in cavity M6 of UEC connector X3. It will be the grey, rear, outboard connector.
• Remove the terminal from cavity M6. It will be a VT/GY wire. Replace it with the smaller of the two terminals, with the shorter wire length on the new accessory harness.

Anyways, I'm gonna try again tomorrow and will post pics of what I find. Worst comes to worst, I can explain in detail what I've tried and searched for to my dealer service crew

Man...can't thank you enough for all this info. It seems to me that it shouldn't be as hard as their instructions make it out to be. I would think that it would be as simple as group of wires to reconnect, but it seems that it's going to be way more difficult than I imagined. Weird.

[kweable]

It's also weird that the light will work when the button is pushed on the dash, but it doesn't when the brake pedal is pressed nor when the truck is in reverse.

[newdude]

It's also weird that the light will work when the button is pushed on the dash, but it doesn't when the brake pedal is pressed nor when the truck is in reverse.

 

The cargo lamps are on a separate circuit that's why they still work but the CHMSL doesn't. Switch those wires in the UBEC as above and she'll function like it never had the roll bar.

[CobraCmdr]

 

The cargo lamps are on a separate circuit that's why they still work but the CHMSL doesn't. Switch those wires in the UBEC as above and she'll function like it never had the roll bar.

 

After reading this, I think I might have been looking for the wrong thing around the UBEC yesterday.

 

So rather than the harness connector, I should be looking for that single (purple) wire that was removed in the UBEC itself, right?

 

I was looking at this connector before:

 

Edited November 15, 2016 by CobraCmdr