Primus Brake Controller Shows O.O When Brakes Applied  

Question:

Expert Reply:

Sounds like there might be some blown fuses, or some shorts on your brake controller/7-way circuits.

The first thing I would do is test the manual override lever when the trailer is connected and see if it will apply the trailer brakes. If it has voltage I would check to make sure the brake switch circuit (red wire) sees voltage when the brakes are applied. If not, you have located the problem and will need to inspect this wire for loose wires or corrosion and fix as necessary.

Next I would test the brake output circuit (blue wire) from the brake controller. The easiest way to test this will be to cut the wire and test for voltage on the side from the brake controller with the manual lever applied. If you get voltage here you know the problem lies somewhere in the wiring between the brake controller and the 7-way trailer connector.

At this point you will want to test the trailer connector for voltage on the brake output circuit of your 7-way. This should be the blade in the 5:00 position. At this point you will want to work from there back to the front of your vehicle checking until you find voltage. Once you have found voltage you have narrowed where the problem is. You will need to look for any loose or exposed wire and corrosion and fix as necessary.

You might also try setting up your brake controller again just to make sure something is not out of adjustment. I attached installation instructions for this product for you to check out also.

expert reply by: Chris O

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