Troubleshooting Trailer Lighting that Pulses When Running Lights and Hazards are On

Updated 05/17/2017 | Published 05/16/2017

Question:

I have a 95 loadking lowboy trailer, the lights on it all work and operate fine. When running lights are on and I turn my hazard switch on it makes the rest of the lights have a slight pulse, hard to notice but DOT noticed. On the lowboy trailer, I have ran all new wire and harnesss, new bulbs all around, new plug at kingpin and new plug at toung, new harness between them. Grounded each light individually making sure all are properly grounded. Went as far as to run a jumper wire between the two pieces. On the truck, I have replaced the plug and traced all wire down, all grounds are properly grounded. Replaced the hazard switch and relay. I have several other trailers I run as well as one more truck and this lowboy is the only one that does it work either truck.

asked by: Paul B

Expert Reply:

With this type of problem it's almost always related to an insufficient ground situation. When a trailer's wiring doesn't have enough of a ground you'll start seeing other circuits behaving weird as the lights are trying to ground through the other light assemblies basically.

It sounds like you cleaned up most of the ground but if there is any way to improve the ground that goes from the frame of the trailer to the trailer wiring harness ground circuit the problem should go away.

expert reply by: Jameson C