Troubleshooting Trailer Left Turn Signal Not Functioning on a Trailer Towed by a 2001 Lexus RX300

Question:

Left turn signal still works on vehicle but after several months it doesnt flash any more on trailer. Tried several trailers but something has failed/faulted in the wiring. The right turn works but then the left flashes alternately... Any ideas?

asked by: Jayson P

Expert Reply:

My first instinct would be to check the vehicle side trailer connector. Any dirt and/or corrosion can cause the harness to function improperly. Give it a good cleaning with a wire brush to clean out and off any corrosion.

If you are still experiencing a problem after cleaning the pins, you will want to check them for the proper functions using a circuit tester like part # PTW2993. If the functions are all correct and working properly then there could be a problem with the trailer wiring, most likely a bad ground. The left turn signal and brake are on the same circuit coming from the connector and the left turn signal may have been shorted at some point which could cause the problem.

If the signals on the vehicle side connector are not correct, further troubleshooting will be required. I would check to make sure the ground (white wire) on wiring, # C59496, is still secure and connected to a clean and corrosion free spot on the frame of your 2001 Lexus RX300. While checking the ground, you can also check for any loose or broken wires.

Next, make sure the red power wire is connected to the battery and that the fuse is inserted and not blown. I doubt the fuse is the problem as the unit would not function at all. But a loose power wire could cause intermittent functionality.

Last, I would check the converter box itself. What you will do is first check the wires going into the converter box for correct functions. If the functions going in are incorrect, there is some sort of problem with the vehicle wiring. If the functions are correct, check the wires coming out of the box for the correct functions. If the functions are wrong, something is wrong with the converter, and it will need to be replaced. If the functions are correct coming out, then somewhere is a bad ground or loose connection you will need to rundown.

I have included a video on circuit testing vehicle wiring and a video on testing a converter box below.