Is Voltage Drop Normal When Testing Brake Output Wiring of Trailer

Question:

2009 Silverado with integrated brake controller. connect to my 36foot gooseneck I tested the volts at the junction box right at the neck of the trailer. I have 10.8 volts then I tested the volts at a junction box between the 2nd and 3rd axle, I get 6.4 volts. Seems like bad wiring or connectors to me. this was done with the engine off and the key On. I tried again with the engine running. The volts at the tongue were the same approx 10.8. but the clincher is the volts back at the rear axle jumped up to 8 volts. My questions: Should not the voltage at the axles be very similar to the voltage at the back of the truck? Seems like it should be reading 12 volts maybe even a tick above am I correct? Why the jump back at the axles, but nothing up front with the engine running?

asked by: Jason P

Expert Reply:

You really should have around 12 volts at the junction box and then about the same at the axles. That amount of voltage drop is most likely due to using wire for the circuit that is too light. Especially since you said you have three axles. I'd replace all of the trailer wiring for the brake output circuit with 10 gauge wire like part # 10-1-1 (sold by foot) or heavier if possible and the decreased resistance will allow the voltage to be where it needs to be. You'll probably notice much stronger braking as well.

expert reply by: Jameson C