Blue Wire Showing Voltage with No Trailer Connected and When Not Applying Brakes on Brake Controller

Updated 09/29/2025 | Published 06/13/2012

Question:

My brake controller light does not illuminate when I have the brake controller installed with confirmed + voltage to the black wire and confirmed ground to the white wire. Should that light be red if the trailer is not hooked up? Also, the blue wire is showing positive voltage without the brake pedal being depressed. When I test that wire for voltage, the light on the controller lights up green, indicating that the trailer is hooked up even though it isnt. Should that blue wire have constant voltage the #2 pin also has constant voltage at the tow vehicles 7-pin connector? Should the red light be on if there is no trailer hooked up and power supplied to the controller? Not sure what this part #5100 is. I have a Voyager Tokensha brake controller

asked by: Bradley W

Expert Reply:

It does sound like there is a short to the brake controller through the wiring or in the internal circuitry of the brake controller. Since your brake controller shows no red light this indicates a short to the brake line (blue wire).

If you are using wiring harness, # 3040-P, make sure that extra white ground wire is attached to a clean bare metal surface. If it is hardwired to the truck, the ground needs to be connected to the negative battery terminal.

Sever the blue wire a few inches back from the controller and use your circuit tester to test the wire. If it shows voltage without applying the manual override, then this indicates a problem inside the controller and it will need to be replaced. If the issue stops, there is a wiring problem somewhere between the controller and 7-Way.

The controller will send a small amount of power back to check to see if a trailer is connected but it should be just a tiny amount. Applying a circuit tester to the wire could trick it into thinking there is a trailer connected because it adds more of a load on the system.

You would need to check to make sure the wiring is intact on the harness and on your truck including the grounds. If you cannot find a wiring or ground issue, then something is wrong with the internal components of the brake controller and it will need to be replaced as there are no internal serviceable parts.

expert reply by: Michael H