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Wiring 12-Volt Accessory Circuit to 7-Way Trailer Connector on 1997 Chevrolet 3500 Cab and Chassis

Question:

I dont have an auxillary wire to do the maintenance charge on my trailer break-away battery. Can I run a wire with a fuse from the truck battery all the way back to the plug on the back bumper? I used all the wires but one on my truck to wire up the 7pin/4flat combo plug on my truck. This chevy truck has one white wire I havent used for anything, its only hot when I hit the brake pedal. BUT when I put my 4 flat wire trailer plug for my small trailer on the truck , all lights work perfect, brake light included. Wonder what that white wire is for??? And I dont have a wire to run to the auxillary spot on my plug for maintenance charge. Or is that the white wire that is only hot when brake pedal is pushed? I dont know why everything I do turns into an epic mission, I just want this thing to work!

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Expert Reply:

I believe the remaining wire you're speaking of is actually light blue, and is meant to provide power for a third brake light installed on a camper shell.

If you want to run a 12-volt accessory power circuit, you can run it from the positive battery terminal to the 7-way. Your truck MIGHT have a 12-volt accessory wire ran already...you'd just need to make the connections on each end. Look on the driver's side frame rail at the rear of the truck. You're looking for an orange wire. If you find it, it would connect to the pin in the 1:00 position in the 7-way. The other end of the wire terminates under the master cylinder. You'd attach a ring terminal onto the end of the wire, and connect it to the positive battery terminal, installing a 40 amp circuit breaker, part # 9510 inline with the circuit. If you can't find the orange wire, you can run your own length of 10 gauge wire, like part # 10-1-1 (sold by the foot) from the battery to the trailer connector.

I've linked you to our trailer wiring FAQ article, which has several different wiring diagrams and photos showing how a 7-way is wired.

expert reply by:
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Mike L

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