Troubleshooting Trailer Taillights that Behave Strangely and Random Circuits Light Up with Blinker

Question:

I have a trailer that I’ve pulled for years I have maintained and fixed all the lighting issues that ever come up -4 wire system -I know what goes where and why… But right now what I have happening is when I turn on my right blinker ,my right blinker on my truck works both my trailer tail lights flash and all the running lights flash , and the left truck blinkers flash weakly..I put the brakes on and it works properly the brake lights come on just the right blinker and running lights blinks but if I turn my headlights on all the running lights come on but don’t blink, and the blinker doesn’t blink on the trailer but it does on the truck..HOLY GUACAMOLE . I had to rent a truck for a week but also had the same trailer hook up and it did approximately the same thing tho not exactly so that makes me think it doesn’t have anything to do with the truck electrical system and I’m guessing it must be some kind of a ground fault somewhere? But the trailer is an enclosed trailer and all the wiring is built into the walls

asked by: Ken

Expert Reply:

What you described is the classic and super bizzare insufficient ground scenario. It's hard to explain how it all works, but basically if you improve the ground wiring of the trailer you'll see that the lights will all come back like they should.

Check the main ground wire that goes from the connector to the frame and then make sure all the lights are grounded properly as well.

expert reply by: Jameson C