Old Primus Brake Controller Just Shows Red Dot with Brake Pedal Pressed on 2004 Dodge Ram

Question:

I have an older unit with no booster installed in a 2004 Dodge. I have it second hand so dont know the history. It was working but now when you push down on the peddle no numbers show on the screen but a red dot appears and flashes. And it doesnt feel like the trailer brakes are coming on. Is there a fuse or

asked by: Roy

Expert Reply:

On the original Primus brake controller the red dot appears either when the manual slide knob is used with no trailer connected or when applying the manual slide after the display flashes n.c. for 15 seconds.

If it is happening but neither of those situations apply then you can test the brake controller to see what the problem is.

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 # PTW2993 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.

If it 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.