Troubleshooting Trailer Wiring that Shows Running Light Circuit Active All the Time

Published 05/17/2018

Question:

trailer running lights stay on after cutting vehicle lights off 4 way plug gets warm. All lights work as they should.

asked by: RawsoShell

Expert Reply:

There's either a short between a 12 volt power source and the running light circuit of your trailer wiring or the converter box of your trailer wiring is damaged and it's keeping that circuit hot all the time.

What you will want to do is test the wires going into the box of the converter box for voltage with a circuit tester like the # PTW2993 to see if there is voltage going into the box when the taillight functions of your vehicle are applied, and then test the output side of the box to see if the current is making it through the converter. If not then the problem is that the converter box has shorted itself out and would need to be replaced.

Before you replace it you will want to inspect the wiring of your trailer to see if you can find anything that would cause the box to short out like corrosion or cut/exposed wiring. These boxes don't usually go out unless there is a short on the trailer that takes it out.

expert reply by: Jameson C