Trailer Wiring Harness Fuse Blown When Headlights are Turned On on a 2007 Toyota RAV4

Question:

I purchased the 118412 wiring harness for my 2007 Rav4. I watched the great installation videos and everything made sense and went according to plan. The initial tests on my trailer were successful. However, I blow the fuse that is located on the wire from the battery. I think its only at night when I turn the headlights on. Ive gone through several fuses. My trailer is for a smaller boat and just has a tail light and amber light on each side. Everything worked fine for the vehicle I sold a few months ago and the wiring on the trailer looks good also. Do you have any ideas? Thank you.

asked by: Cory

Expert Reply:

It sounds like there is a problem with the trailer wiring that you installed on your RAV4. I would start by removing the trailer connector and checking each wiring connector to make sure a pin was not bent of broken when installing the harness, causing a short.

Next, without the trailer connected, test the wires going into the converter on both sides with a circuit tester to see if power is going into the converter properly with each signal activated and the tail lights on, and coming out of the converter. If it is functioning properly without a trailer connected, and the fuse does not blow when the taillight circuit is activated, then there is a wiring problem on the trailer. If there is power going in correctly and not coming out correctly or blowing the fuse without a trailer connected, the converter has been shorted and will need to be replaced.

While you are checking the circuits, make sure there are no pinched or rubbed wires in the harness. If the converter has to be replaced, you should check the trailer wiring closely before connecting it back to the vehicle, or you may cause a short circuit situation again and have to replace the wiring harness again.

We have a video on how to test the converter for proper function, see link.

expert reply by: Robert G