Primus Brake Controller Display Shows 17 with Brake Pedal or Manual Override on 2004 Ford Expedition

Question:

I hooked up the controller to a 2004 Ford Expedition and everything seemed normal until I hooked up my Keystone RV Passport. I get the normal C showing connection but when I depress the brake pedal It only displays 17. Also, when I use the manual control it only show 17 no matter how much I depress the switch or adjust the voltage knob. I did see the notice about the Stoplight wire connection, but I do not have a light green wire on the switch I have a red with green strip and black wire.

asked by: John P

Helpful Expert Reply:

It sounds like there are a couple of issues going on with your brake controller. It actually sounds like you have the OL error (maybe) and that would indicate an overload condition. I could not find any error for the Primus controller that was even close to the 17 that you are seeing. This makes me think that there is also something wrong with the display.

To determine the issue there are some tests you can do. In the truck cab you will need to sever the blue wire several inches from the back of the controller. Then use a circuit tester such as # PTW2992 to test the end of the blue wire coming out of the controller. It should only have power when you apply the manual override. If it shows power at idle, then there is something wrong with the controller and it will need to be replaced. Also, the red wire should only have power when you step on the brake pedal. If it has power all the time or if the headlights or turn signals are on then it is likely not connected to the right wire on the vehicle.

If the blue wire tests fine then reconnect the blue wire. Then move on to the truck side trailer connector. Many times, dirt or corrosion can cause a short in a trailer connector. Make sure the truck and the trailer side connectors are clean and free of corrosion inside and out.

You can test the brake output pin and it should only show power with the manual override. If it shows power any other time then there is a short somewhere between the connector and the brake controller you will need to track down.

If the truck side checks out fine then it could be the wiring to the brake magnets or the magnets themselves. Inspect the power wires to the magnets and look for pinched, frayed, or damaged wires and fix as needed. Make sure the ground wires are attached to clean and corrosion free bare metal surfaces.

You can visually inspect the magnets and if you can see the copper windings coming through the magnets will need to be replaced. To further test the magnets you can follow the help article I have linked. I have also included some help articles on testing and troubleshooting brake controllers for you.

expert reply by: Michael H