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Primus Trailer Brake Controller Shows N.C when Installed on a 1997 Ford F-150


I have a 1997 f150 and purchased the 90160 with the adapter harness. When I put it into the truck the code that comes up is n.c. Does the harness conect color to color or is there a different wiring diagram?

asked by: Travis

Expert Reply:

There are 4 possible reasons why the Tekonsha Primus, # TK90160, is telling you N.C.

1. Trailer not connected to tow vehicle.
2. Trailer connected with open circuit on brake line.
3. Trailer connector disconnected or corroded.
4. Loss of trailer brake magnet ground.

The first one is easy enough to solve so we will go on to the second possible issue. An open circuit on the brake line or a short to the brake circuit could be caused by a couple of different issues. First, it is possible that there is corrosion or dirt in the trailer connector (see number 3 above) and that is causing a short from the 12 volt circuit to the brake circuit.

Corrosion can also build up behind the connectors where the wires attach where you cannot see it so be sure to check that as well. Check both the vehicle side and trailer side connectors.

If it is still showing N.C. then test the brake controller itself by severing the blue wire behind the controller. Use a circuit tester like # 3808 to test the brake controller end of the blue wire. It should only show a signal when the manual override lever is applied on the brake controller. If it shows a signal all of the time then there is something wrong with the internal circuitry of the brake controller and it will need to be replaced.

If the brake controller checks out then you could have a problem with the trailer brake magnets. To test the brake magnets you can start with a visual inspection. If you can see the windings coming through then the magnets will need to be replaced. To further test the magnets I have included a link to an FAQ article that will help.

expert reply by: Michael H

Michael H

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