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2500HD/3500 HD Trucks & Drivetrain Discussion Forum for the 2001 & newer 2500HD/3500 Trucks, Transmissions & Drivetrain

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  #1  
Old 09-11-2017, 08:43 AM
Yukon6.2 Yukon6.2 is offline
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Default 2002 rear wiring diagram and colors

Hi All
I am looking for a wiring diagram for the rear taillight harness.
My new to me tow truck is a 2002 GMC 3500 and someone has done a butcher job on the wiring for the wrecker deck.
I want to clean it up and would like to get a diagram or at least a description of what each color wire is supposed to do.Right now when use one of the turn signals it flashes both sides,but use the other side and it works fine.I would like to have all OEM wires doing what they are supposed to do,plus be able to hook up a brake controller.
Thanks for the help
Thomas
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90 Chev 3500 c/c 4x4,6.2na,400 auto,4:10 gears.DSG Timing gears,main girdle, isspro tach, pyro,boost,oil and trany temp.Dual Tstats, High volume peninsular pump,on shelf, Custom turbo and intercooler 85%complete. Change of plans for the dually, it's going to get a Cummins. Both trucks are Blue 90 4x4 crews
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  #2  
Old 09-11-2017, 10:26 AM
rapidoxidationman rapidoxidationman is online now
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Maybe one of these is the one you're looking for?
http://www.revbase.com/BBBMotor/Wd/R...WdSubsystem=20
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  #3  
Old 09-12-2017, 08:35 AM
Yukon6.2 Yukon6.2 is offline
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Thanks that helps some.
I was hoping to find a breakdown on the different colors in the rear harness and what they do.
This was a dually P/U but the rear junction block has been removed and the harness has been spliced into.An Aftermarket junction box had been used on the wrecker deck,which has been damaged and there are way to many wires clumped together that don't really need to be there.
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90 Chev 3500 c/c 4x4,6.2na,400 auto,4:10 gears.DSG Timing gears,main girdle, isspro tach, pyro,boost,oil and trany temp.Dual Tstats, High volume peninsular pump,on shelf, Custom turbo and intercooler 85%complete. Change of plans for the dually, it's going to get a Cummins. Both trucks are Blue 90 4x4 crews
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Old 01-20-2018, 11:56 AM
Yukon6.2 Yukon6.2 is offline
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Help
So i opened up the rear harness yesterday and discovered way more wires than i thought would be there.
Large gauge red,white and blue
Small gauge black,yellow,light green,med green,dark green, med blue,2x light blue,dark blue,2x brown and a brown with white stripe.
I would like to find out what they are all for so i can utilize as much of the stock harness that i can.I have already pulled out about 3 runs of wires that wern't stock and were doing nothing.
I come up with 15 wires so i imagine that some must be for trailer brakes and trailer charging.So if anyone knows if this truck would have factory wiring for trailer brakes could you steer me towards where i could find that as well.
Thanks
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90 Chev 3500 c/c 4x4,6.2na,400 auto,4:10 gears.DSG Timing gears,main girdle, isspro tach, pyro,boost,oil and trany temp.Dual Tstats, High volume peninsular pump,on shelf, Custom turbo and intercooler 85%complete. Change of plans for the dually, it's going to get a Cummins. Both trucks are Blue 90 4x4 crews
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  #5  
Old 01-20-2018, 01:18 PM
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DmaxMaverick DmaxMaverick is offline
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Careful, you might complicate it.

The large wires are the trailer power and ground. Verify each with a VOM (no telling what they are if they've been "helped").
White = Ground
Blue = Brakes
Red = 12V power

The small wires are (standard) trailer chassis lighting. The basic colors (lt. blue vs. dk blue, stripes, etc.) are the same, only left and right.
Yellow = Left turn
Green = Right turn
Brown = Tail/clearance/marker

The power distribution (fuse) box under the hood will have each of these circuits fused, individually. Verify each is connected accordingly before connecting the terminal ends and adding power to the fuses.
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  #6  
Old Yesterday, 11:20 AM
Yukon6.2 Yukon6.2 is offline
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Thanks that helps a bit.
I assumed that nowadays it would be easy to find this info online,but i didn't come up with much.Probably wrong terms for searching.
I didn't want to complicate things that was my objective.This truck has a wrecker deck on it and the wiring was freaking mess.I hate others wack job wiring.So i wanted to eliminate any wiring that was redundant ,and use as much of the factory harness as possible.
Unfortunately while working on this project i found a new one.Previous owners had installed a remote start/security system.And it still powers up because i found this stuff when i had the dash off,and when the ignition is turned on a little red light comes on a little black box which is glued to another black box with lots of wires and relays that arn't GM.
So someday when i am bored or the truck dosn't start i will be trying to surgically remove it and fix the wires where they were hacked into,Urggg.
So DmaxMaverick could you tell me where i could find the cab end of the trailer brake harness?
Thanks i appreciate the help
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90 Chev 3500 c/c 4x4,6.2na,400 auto,4:10 gears.DSG Timing gears,main girdle, isspro tach, pyro,boost,oil and trany temp.Dual Tstats, High volume peninsular pump,on shelf, Custom turbo and intercooler 85%complete. Change of plans for the dually, it's going to get a Cummins. Both trucks are Blue 90 4x4 crews
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  #7  
Old Yesterday, 02:06 PM
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DmaxMaverick DmaxMaverick is offline
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The trailer brake harness junction is in a panel on the firewall, between the E-brake pedal and the brake pedal. It may have a cover (about 4-5" square). The trailer brake controller slot, IIRC, is the top row, second from the left on the 01-02. Get the trailer brake controller harness (GM part, or aftermarket compatible) and it will only fit the correct slot. If it is missing 12V power to the rear chassis harness (trailer 12V), there's a 40A maxi-fuse that needs to be installed in the under hood fuse box. Originally, the 01-02 models with the towing package had the harness, with fuse taped to it, included at delivery (usually in the glove box).
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