Wire Gauge for Brake Controller Installation in 42-Foot Diesel Pusher Motorhome

Updated 04/28/2016 | Published 04/24/2016

Question:

I have a 42foot diesel pusher motor home. I will be towing a pontoon boat. I intend to convert to electric of hydraulic brakes. Batteries, etc. are all located at the rear of the coach. I have found, I think, the wire that comes from the front of the coach to the plug at the back. I think it is there for a brake controller. The wire is not a sufficient gauge to carry 40a. I am thinking of using the brake controller and the existing wire to operate a 12v contactor/relay that would supply 12v to the electric over hydraulic controller from the batteries. This would alleviate having to run a #10 wire from the back to the brake controller then back to the hookup at the back of the motor home. I am also concerned that over 80 feet of #10 might have a voltage drop.

asked by: Dale M

Expert Reply:

You are correct that 10-gauge wire like # 10-1-1 might be inadequate to deliver brake controller output power to a trailer connector that is upwards of 70 to 80-feet from the controller's location in the motorhome cab. For a wire run of this length I suggest doubling up the 10-gauge wiring from the controller's blue output wire to the trailer socket on the MH. This should prevent voltage drop and allow full braking power to reach the electric-over-hydraulic (EOH) brake actuator on the trailer.

The trailer 12V auxiliary power circuit, which maintains your charged trailer batteries, should still be fine with one run of 10-gauge since this circuit will not have to run the full length of the MH, just from the rear-mounted battery to the trailer connector.

We have not done an install with a contactor/relay set-up like you're describing but this could work so long as the EOH actuator you choose will be compatible. I suggest checking with the manufacturer of the system you're considering to make sure such an install is not going to void the unit's warranty.

Not all brake controllers work well with EOH braking systems but one that will work just fine is the Tekonsha Prodigy P2 # 90885. This reliable performer offers settings for both electric drum brake and EOH actuator operation.

expert reply by: Adam R