How to Test a Malfunctioning Trailer Wiring Harness on a 2006 Toyota RAV4

Question:

I have a good connection to ground and battery. So at the rear of the vehicle where Ive run my 12V from battery and grounded at the chassis, I get around 12.6V just like at the battery. Thats going into the black box controller. I plug in the T-connectors to R and L taillights. With lights off, signals off, and brakes off, I get under 12V on brown, yellow, and green pins relative to the white ground. Turn the lights on and I get 12.6V on brown and the same just under 12V on yellow and green. Shouldnt I get 0V on yellow and green? Same thing with brakes and signals. I get the right 12.6 jumps but everything baselines at just under 12V. Again, my ground and power are good. I checked the voltage at the black wire running to the battery and the connection point where I connect the white ground from the controller. Is the controller bad? Thats all I can figure!

asked by: Mike

Expert Reply:

Are you getting power to the wires leading into the box or leading out of the box? On a Curt powered converter it is not unusual to have a little voltage on the output side. There very well could be voltage on the input side but that full voltage should not be creeping out to the 4-Way. If it is then the converter is bad and will need to be replaced.

So what we need to figure out is how the voltage going in compares to the voltage coming out. Use your tester to make sure the signals are correct going into the box. If they are not then that indicates a wiring issue on the vehicle. If they are correct going in but not at the 4-Way then there is a problem inside the converter.

If the signals are correct going in and coming out to the 4-Way then as long as you have around 12 volts on all circuits when appropriate on the output side then it is working properly. I have included a couple of links to the right to help you troubleshoot.

expert reply by: Michael H