Should Red Wire for Primus IQ Brake Controller Always be Hot

Question:

2001 Chevy Suburban 1500 V8 Q vin using Primus IQ The brakes on the trailer are always on while the vehicle is on off only when the vehicle is off. Swapped out the controller with a brand-new controller out of the box, no change of condition, so the controller is good. Following the instructions on several QandAs, I tested the wiring. Blue, isolated from vehicle, is always 10.6 V while the vehicle is on, ramps up to 10.9 V when the slide is activated. Since I already confirmed the controller is good with the swap-out, something else is going on. I pulled the red wire, discovered it is 0.05V while vehicle is off, but 12.6 V while the vehicle is on, Whether the brakes are depressed or not i.e. no change when pressing brake pedal. So I am thinking that is the culprit? The red wire shouldnt be hot all the time, should it? So am I looking at a short on red in the dash or engine compartment or even at the brake pedal?

asked by: Oscar

Expert Reply:

You definitely did find the culprit!

The red wire should only get hot when your brake pedal is pressed. This tells the Primus IQ # TK90160 that you are stepping on the pedal so that the controller, in turn, will activate the brakes on your trailer.

Check for any places where that wire is damaged and try to repair it as that would be the problem. If you can't find any places where it looks damaged then you may need to use something like the Pacer Performance 3rd Brake Light Logic Module # PP20-702 and route this wiring to the red wire on the Primus IQ controller.

This would be the same case if you are using the adapter # 3025-P as well.

expert reply by: Jon G