Trailer Turn Signals Both Blink at the Same Time When Right or Left Turn Signal is Turned On

Expert Reply:

If both turn signals blinking at the same time is a new problem that has occurred after the harness had worked fine before, there are a couple of possibilities that may be causing the issue. First, the easiest thing to check are the trailer connectors. You will be looking for any dirt or corrosion build up in one or both connectors (vehicle and trailer side). Clean them out if you find any dirt/corrosion and see if that helps.

If you still have the problem, disconnect the trailer to test the 4-Way on the vehicle using a circuit tester like # ALL640595. First, test the wiring going into the convert box on # 118426 from the vehicle tail light wiring. If the signals are not correct then you have a problem with the vehicle wiring.

If the signals are correct going into the converter, test the wiring coming out for the correct signals. You would have to test by probing both turn signal wires with only the left or right turn signal in the vehicle turned on. If you find that the signals are incorrect coming out of the converter then the converter has gone bad and it will need to be replaced.

If the signals are correct coming out of the converter to the 4-Way then the issue is on the trailer side wiring. You will need to check the grounds at the trailer connector and the trailer lights. All grounds should be attached to clean, bare metal surfaces.

expert reply by: Michael H