Troubleshooting Tekonsha Primus IQ Brake Controller Not Connected Error

Question:

My tekonsha primus iq brake controller is telling me that my trailer is “nc” not connected to my truck but all of the signal lights are working fine. I have tested that I am getting power to the pin on the truck when I engage the brake controller but it flashes the “Mc” message instead of increasing numbers as I increase the “braking”. I have even tested it on another vehicle that gives the same message that the trailer is not connected and the lights are on. Hopefully you can point me in some direction that is helpful ! Thanks for your time.

asked by: Adam

Expert Reply:

Since you have tested your Tekonsha Primus IQ # TK90160 brake controller on two separate trucks the problem is likely on the trailer side although you should go over each of the troubleshooting steps just to make sure.

To test the brake controller, sever the blue wire a couple inches from the back of your controller. Then use a Circuit Tester like # PTW2979 to test the end of the blue wire coming out of the Primus IQ It should only have power when you apply the manual override; if it shows power at idle then there is an issue with the controller and it will need to be replaced.

If the controller tests fine, reconnect the blue wire and move on to the truck side trailer connector. Often, corrosion or dirt may be the cause of a short in a trailer connector. Check the plug to see if there is any type of corrosion built up that may be hampering its functionality.

You will also want to test the brake output pin on the 7-way socket; 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 find and repair.

If the truck side checks out then it could be the wiring to the brake magnets or possibly the magnets themselves. Inspect the power wires to the magnets and look for wires that may be pinched or otherwise damaged and fix as necessary. You'll also need to make sure the ground wires are attached to bare metal surfaces and free of any paint, dirt or corrosion.

You'll want to visually inspect the magnets; if you can see the copper windings coming through the magnets will need to be replaced. To test the magnets use Multimeter # PT89ZR and follow the help article I have linked to guide you.

I have also attached some help articles on testing and troubleshooting brake controllers for you to check out.