Troubleshooting Voltage Drop on Electric Brake Wire on Trailer with New Wiring

Updated 07/22/2014 | Published 07/21/2014

Question:

I installed 2 new magnets on one on each drum , new wire 14 gauge,replaced brake controller.Useing a continuity tester Im getting continuity between both wires and trailer frame,and a connection between the two magnet wires themselves and very low voltage at brake drum.All my trailer lights work good,then it was a matter of three wires for electric brakes.One wire from each magnet went to white and grounded at front of trailer,the other magnet wire went to black,connected to a blue from brakeaway switch,and both of those connected to the blue electric brake wire on trailer plug.I double checked the color code on trailer plug with diagram on the cover of plug on my truck I bought from a ford dealer and is the 7 pole RV type.Ive double checked all my connections and dont understand why Im not getting power to the magnets.Is the 14 ga. wire causing a voltage drop enough to not activate the magnets?? or could the brake away switch be shorting out? if so,how can I test it?..........stumpt

asked by: Ron G

Helpful Expert Reply:

The first step I would take is to replace the 14 gauge wire for the electric brakes with either 10 or 12 gauge wire. It is not recommended to use wire smaller than 12 gauge on electric brake and battery charge circuits on trailers. The smaller gauge wire should not cause a significant voltage drop by itself, but it could easily overheat and cause problems in the future.

The next step would be to inspect your ground connections. Be sure everything is grounded to a clean, bare metal surface. Once you are have the larger wire ran and you are absolutely sure the grounds are good, use your tester to see where the voltage drop occurs.

I would start at the 7-way connector on the truck. Test each pin to make sure you have sufficient power for each function. I have attached a diagram that shows what the function of each pin should be. If the truckside connector has the correct power output, then plug in the trailer and test the electric brake wire starting at the 7-way connector. Probe the wire at different points working your way back to the brake magnets. Once you find the where the voltage drops on the trailer, you should have a good idea on what is causing the problem.

expert reply by: John H