Troubleshooting Trailer Taillight Blinkers that Both Flash When Either is Applied

Question:

On my 2005 Ford Ranger 4/4 I hooked up a 4 wire trailer plug. The park lights work fine but when I Put a turn signal on all of the park lights flash on the trailer. When the park lights are turned off with a turn signal on it’s the same result. There are no break lights on the trailer at all. I am guessing this is a converter box problem. Where is the converter box on a factory installed package? Do you have a part # for a new converter?

asked by: Rick P

Expert Reply:

First thing you should do at this point is test the 4-way of the wiring harness with a circuit tester part # PTW2993 for voltage on all of the right pins when the taillight signals are being applied. Just like in the video I attached.

If the voltage checks out there but the trailer lights still don't function right then the problem is on the trailer wiring. That would mean that problem is either due to a ground issue or a short issue. I suspect you have a short between the blinker circuits which is causing them both to flash at the same time.

expert reply by: Jameson C