Primus IQ Trailer Brake Controller Only Shows 4 Volts Output on the Blue Wire at Trailer Connector

Question:

Why is it that i can only get a maximum of 4 volts from the blue wire at the end of the trailer pin? i have the Primus IQ.

asked by: Adam

Helpful Expert Reply:

There could be several reasons you are not getting the correct voltage from your Primus IQ brake controller # TK90160. First, make sure that you have the power output setting appropriately adjusted. This seems like a no-brainer but sometimes the controller can get bumped and the the setting could change without you knowing.

Another possibility is that if the controller is not mounted within the range described in the instructions, linked for reference, it will not operate correctly. The controller can be mounted between 0 degrees (parallel with level ground) or 70 degrees nose up. It cannot be tilted or turned to one side.

To further test the brake controller you will use your tester to measure the voltage on the blue wire at the back of the controller. To do this sever the blue wire several inches from the back of the controller and test the end coming out of the controller. Fully apply the manual override with the controller set to maximum voltage. You should get around 12 volts.

If you do not get the proper voltage and the controller is mounted properly this indicates a problem inside the controller and it will need to be replaced.

If you do get the proper voltage at the controller reattach the blue wire and test again at the connector at the back of the truck while someone else fully applies the manual override. If you still do not get the proper voltage then that indicates a problem on the blue wire somewhere between the controller and the connector.

Check to make sure the connector is clean and corrosion free inside and out. Then you can trace the brake output wire (in the 7 oclock position if looking at the back of the connector) forward and fix any loose connections or frayed wires.

I have included a couple of links on testing brake controllers.