Morning,

The most likely culprit is the ground, so pay particular attention to the white lead.

The one important thought I will share is you can not check out many brake controllers at all by using a multimeter at the contacts on the truck. The controllers has to "see" a "load" to function correctly, and a multimeter does not create an ample load.

I do not know if that is the case with your controller. It is increasingly common, however, with modern controllers. If your controller falls in that category, the voltage readings you are seeing are meaningless and tell you nothing at all about the controller.

When I work on brake controllers, I use a tester that emulates all of the resistances (loads) found on a standard trailer and I test brake output with amperage, not voltage. Many RV dealers have the same device and since it takes only a minute, the ones near me don't even charge to plug it in and read the outputs. If you do not want to go that route, pick up one of the seven pin testers readily available at many automotive stores. Any time you see a technician using a multimeter to test a brake controller, be very careful.

You may not be able to compare readings between vehicles unless you are comparing the same controller mounted in the same vehicle.

I guess this is my very long winded way of saying not to try to fix it until you're sure it is broken and using a multimeter to test brake controllers can get you chasing ghosts.


Best of luck,

Steve