Troubleshooting Brake and Turn Lights on a Trailer with 7-Way Plug

Updated 02/28/2018 | Published 02/27/2018

Products Featured in This Question

Hook Probe Circuit Tester

(62)

$13.94

Dielectric Grease for Electrical Connectors, 2 oz.

(1486)

$10.91

Question:

Trailer lights are wired with a seven pin rv plug. Right side lights all function correctly. Left side has parking and markers but no brake or turn signals. Both lights function. I checked the truck with a seven pin connector test plug everything functions. I even added a ground to the truck from trailer no difference. There are no shorts. Wires ring out with voltmeter. I thouht maybe since each side has an led replacement that switching power leads to light fixture would make a difference. All this did was make the light flash when right side was activated with right turn signal. Im overlooking something.Any help would be appreciated.

asked by: James M

Expert Reply:

At this point, you'll want to follow the physical wire from your connectors at the nose of your trailer all the way through the frame and body back to the left (driver's) side, checking its power as you go. It's really easy to do this with a probing circuit tester like part # PTW2993. Chances are that there's an issue on the wire somewhere that it's being kinked, pressed or had its insulation rubbed away. Since it sounds like you've checked everywhere else, there has to be an issue somewhere on this circuit on the trailer.

One of the easiest things to overlook is the actual grounds for the lights on the trailer. If these points are corroded or have been painted over, they can stop operating. To fix it, you'll simply reposition to a clean, unpainted section of the trailer frame and reinstall the ground with a self-tapping screw.

Since you've already got a handle on the wiring, it's not a bad idea to clean all of the connections and apply dielectric grease (available as part # 11755) again to ensure continued operation after this problem is solved.

If you're suspicious that there may be corrosion inside your trailer plug, you can replace the 7-way with a new J Box, part # HM50002.

expert reply by: Jacob W