Should the Blue Wire On a Trailer Brake Controller Always Show 12 Volts of Power

Question:

i am wondering why the blue wire has 12 volts when the trailer is not connected ? the system works fine when the trailer is connected and if this is normal do all brake controllers operate this way? thanks

asked by: Scot

Expert Reply:

A brake controller sends voltage back along the blue wire to sense if a trailer is connected or not. However, 12 volts is very high for this function and there may be a short to the blue wire. You can test the controller by severing the blue wire a few inches from the back of the controller. Use a circuit tester, like # 3808 if needed, to test the end still attached to the controller. It should only show a signal when you apply the manual override. If it shows a signal at any other time then there is a short inside the controller and it will need to be replaced.

If everything test normal then the most likely culprit is a dirty or corroded trailer connector. Check the vehicle side trailer connector and clean it out. Corrosion can also build up at the back of the connector where the wires attach.

expert reply by: Michael H