Troubleshooting Prodigy P3 90195 Brake Controller That Goes Dark When Manual Override is Pressed

Question:

I have the Tekonsha PIII brake controller. I hooked it up to a trailer that I believed shorted out some wiring in my truck. The controller went black. I moved the power wire to a different spot and the controller powered back up. But now when you hook up to a trailer and use the manual lever it kicks out and goes dark. I release the lever and it resets. I can here it click inside the controller. It also showed the trailer still hooked up after we unhooked it? Thanks.

asked by: Heath G

Expert Reply:

There may still be a short in the trailer wiring that is causing the erratic behavior from the controller.

You can test by unplugging the trailer connector from the truck and pressing the P3's manual override lever again. If the controller goes dark again, even without the trailer connected, then this suggests that there is internal damage to the Prodigy brake controller or a problem in the truck's wiring. If the P3 acts normally (remains powered up) when you apply the manual override then this suggests that you still have a wiring issue on the trailer.

You can also test the trailer directly when it is disconnected from the truck. Use the truck battery or a spare 12V battery that is well charged to apply power to each trailer circuit one at a time. This will allow you to test all the lighting circuits and the trailer brake circuit independent of the vehicle and brake controller's wiring.

When you apply 12V power directly to the pin for the brake circuit (see photo please) you should hear the brakes react with a gentle hum. If you jack up one side of the trailer you can also test that wheel by hand to see if the brakes hold it steady as they should when full direct full power is applied.

Wiring faults in a trailer can damage a brake controller and/or blow fuses in the vehicle in some circumstances so you'll want to ensure your trailer is fine before using it with this or any other vehicles. Since the P3 still shows a trailer is connected when one is NOT, this suggests a problem in the truck's 7-way socket. If there is corrosion inside the socket (which can be hard to spot from the outside) this could cause two separate circuits to be bridged together and cause this issue.

expert reply by: Adam R