Primus IQ Trouble Shooting Brake Output Power Only When Truck Lights Are On

Question:

I have had this problem ever since I installed the primus IQ on my 2004 GMC Sierra 2500hd about a year and a half ago. I just replaced the wiring harness with a new 7-way junction box in the bed of the truck hoping this would solve this problem. When the truck and trailer are hooked up sitting in the back yard, I have a power to the brake controller of 1.8. and the brakes are humming. This power of 1.8 also appears when the trailer is not hooked up. I have noticed this is true when the lights are on. If I turn the lights off, it goes to where it was previously set and shows .c. and the brakes are off not humming. Please note that the trailer fifth wheel has not been moved for about 3 months. Can you give me your thoughts.

asked by: James F

Helpful Expert Reply:

It sounds like there is a short in your wiring when you turn your lights on. It is pushing more power to your brake output wire. I recommend using a circuit tester like # PTW2993 to test the cold side of your brake switch (red wire). If there is a draw there, then the switch or the ground wire are the issue. The solution is most likely a bad ground, so you will need to check when your lights are on as it won't appear when they are off. The first ground I'd check is the ground to the Primus IQ brake controller # TK90160. You can run a jump wire from your battery directly to see if this is the issue.

If not, let me know and we can do more troubleshooting.

expert reply by: Jason S