Troubleshooting Tekonsha Primus Brake Controller Error and Constant Brake Magnet Power

Question:

P.L. is displayed on the brake controller, and when that eventually goes away I have constant power going to the trailer brakes. Even while not breaking. Where do I start troubleshooting this? Thank you

asked by: Kody N

Expert Reply:

The Tekonsha Primus IQ Trailer Brake Controller # TK90160 is displaying that there is a power interruption while brake pedal is depressed. To troubleshoot that issue, you will need to use a circuit tester like # PTW2993 to probe the red wire coming out of the brake controller. It should have power when you hit the brake pedal and no power when you do not. If you have no power at all on that wire when you depress the pedal, you will want to make sure there is power getting to the switch. If there is power getting into the switch, but not coming out, then you will need to replace that switch.

For the constant power at your trailer brakes, it sounds like there is a separate issue. I recommend using a 12V battery to test each function of your trailer at the trailer connector first. If each function works there, then test each function on the vehicle side of the connector. It sounds like there may be a short between some of your wires that would need to be replaced using # 10-1-1 wire. You will need to make sure each function is isolated on the vehicle side and trailer side and then finally clean the connectors on each side using some sandpaper or steel wool to ensure there isn't corrosion bridging the pin connections.

I've attached a couple articles on wiring of connectors and brake magnets to assist in your troubleshooting.

expert reply by: Jason S