How to Test Trailer Wiring to Find Short Between Two Circuits

Published 08/30/2018

Question:

RV brakes run fine during the day but when I switch on my headlights in my truck and all the trailer lights come on so do the brake lights. I tried switching the wires around at the brake lights that was not my problem. Also it seems when the blinker is on during the day all the lights blink. Can you please Help me

asked by: Jordan W

Expert Reply:

First we need to find out if the problem is your tow vehicle wiring or your trailer wiring. To do this use a circuit tester like part # PTW2993 to test all of the pins on your 7-way for the correct function compared to the diagram I attached.

Next use a jumper wire from a 12 volt battery post to apply voltage to all of the pins of your trailer's 7-way to verify all of the circuits are working like they should. If you see more than one circuit apply when this happens there is a short between those two circuits and you'd have to trace the wiring to find where the short is and fix as needed.

expert reply by: Jameson C