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Old 02-25-2009, 12:14 PM
bczoom bczoom is offline
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Trailer wiring harness instructions

This applies to GM trucks. Not sure about others.

Starting with the all new 2007 Full Size Utilities there is no longer an electric trailer brake controller pigtail harness. The trailer brake controller wiring is now part of the I/P wiring harness and the blunt cut wires are located under the left IP, behind the DLC. There are four blunt cut wires in this harness which are:

Wire Color
SI Document ID #

12 Volt power supply (30A Stud 2)

Dark Blue
Trailer brake output voltage


Light Blue/White
Stop light input

Note: The Red/Black circuit 242 must be connected to Stud 2 30 Amp of the UBEC. The wire is located between the left fender and UBEC. Do not confuse this circuit with 742 (Doc Id 1762158) which is also Red/Black taped to the harness under the master cylinder, which is the 12 volt supply to the 7-way trailer connector and connects to Stud 1 40 Amp.
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Old 02-25-2009, 04:50 PM
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jwstewar jwstewar is offline
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Re: Trailer wiring harness instructions

Watch out on that Stop Light output. It is a very thin wire with a very thin very light blue line. Ask me how I know and I'll point you to another thread.
Racing the only real sport - everything else is just a game.
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Old 02-24-2018, 03:04 AM
CREMA CREMA is offline
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Re: Trailer wiring harness instructions

Thanks for this guide. I have gained some insights to apply to my towing business at Fairfax. It is through these communities that we get to learn a lot.
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