Why Does the Brake Output Circuit of Trailer See Intermittent Voltage When Connected to Tow Vehicle

Question:

black wire out of 50-85-313 going to red on pig tail back to truck, white wire out of 50-85-313 grounded to trailer, blue wire out of 50-85-313 going to black wire on switch, other black wire from switch going to blue wire from pig tail, which is spliced to another blue wire going back thru tubing in trailer, with a brown wire for tail lights, green wire for turn signal, and yellow wire for other turn signal, the last three wires all blink and light up and the blue wire comes on for about a second or two on goes out when i test all wires with test light with 7 way plug hooked to truck. i have a 2010 hd 2500 gmc. could you tell me what i am doing wrong? i purchased all new brakes, hubs, spindels, and wheels from e-trailer and had no problems installing all of them, but this is driving me crazy. if you would like to call instead of e-mail my cell # is 816-305-6924 or home 816-524-2378. thanks for your help.

asked by: Roger G

Expert Reply:

Based on what you described it sounds like you have everything wired up correctly. The first thing I thought of when you described the intermittent voltage you are seeing is that brake controllers will send a small amount of voltage back on the brake output circuit to test to see if a trailer is connected.

Have you tried driving the trailer and seeing if everything works correctly? Everything might be wired correctly as-is and you would be ready to go.

I attached an FAQ on breakaway systems and trailer wiring for you to check out.

expert reply by: Jameson C