Wire a Trailer for Electric Drum Brakes

Published 02/04/2015

Products Featured in This Question

16-Gauge Bonded 3 Wire - per foot

(42)

$1.55

10 Gauge Wire - Blue Primary - Per Foot

(104)

$1.77

35 Ft 4-Way Trailer Wiring Harness - Wishbone Style - 42" Ground

(847)

$23.06

Pollak Black Plastic, 7-Pole, RV-Style Trailer Connector - Trailer End

(692)

$7.94

Question:

I need to rewire my car trailer with elec brakes. Since I need to run a yellow/brown to the LR and a green/brown to the RR.. Why dont they make a 2 wire bonded parallel in those colors? All I can find is the bonded 4 wire.

asked by: Andy M

Expert Reply:

The normal color wire for electric trailer brakes is blue. It sounds like you are using regular tail light wiring, which would not be sufficient size for trailer brakes. Yellow/brown and green/brown to me sounds like parts of a wishbone harness.

A wishbone harness has 2 running light wires instead of one so you don't have to run a jumper wire from one side of the trailer to the other. An example of this type of harness is # A35W42B.

The yellow wire would be for left turn signal/brake lights (since they are combined on the same circuit on a trailer) and the brown wire would be the running lights for that side. Green would be for the right turn signal/brake lights with the brown being the running light wire for the right side.

You would not use the combined brake/turn signal wiring for the trailer brakes because they would pulse the brakes when you used a turn signal. And if the trailer does happen to have separate amber turn signals you still wouldn't tap into the brake light only circuit because it would apply the trailer brakes on full no matter what the braking situation was.

You would use wire # 10-1-1 for electric brake wiring. The trailer connector would have to be sufficient to accept an additional circuit so you couldn't use a 4-Way. The most common is a 7-Way such as # PK12706. The tow vehicle would also need to have a matching vehicle side connector and a brake controller.

I have included a couple of links that should help you with this project.