Why Would Install of Brake Controller Keep Vehicle Engine On

Updated 03/31/2025 | Published 03/09/2025

Question:

The brother has a 2011 Freightliner Coronado that we are wanting to get the electric brake controller to function. The person who installed the controller pulled power from ones of the power studs in fuse panel not directly from battery. They also grounded it near the fuse panel and not directly from the battery. Lights were pulled from rear tail lights of the truck. Controller sensing wire was connected to the brake relay in the fuse panel. Lights work and the controller seem to work until it is connected to the trailer Using a tester. Once connected to trailer, it sill displays open ground sometimes. Trailer brakes do not work, and then after trying them a couple of times, the truck will not shut off until the trailer is unhooked. Appears there is bleed back. Is there a diode or something needed for the lighting? Why no brakes? Rear truck lights are single lamps. Do you have a video for installing one? Should the sensing wire be positive or negative, or doesnt it matter? Thoughts.

asked by: Randall R

Expert Reply:

Hey Randall, I would go through and redo most of the wiring of your controller as the current setup is pretty bad. I've never heard of a brake controller preventing a truck from turning off so that's pretty crazy.

I would take the power wire for the controller and run it straight to the battery's positive post and then also do the same for the ground to the negative post. I wonder if your power wire is on an ignition circuit and it's somehow keeping the ignition active via a backfeeding situation. I would start there and see if it gets any better. Let me know how it goes.

expert reply by: Jameson C

Randall

3/22/2025

We performed a number of changes. 1) As we discussed before, we thought there was some sort of bleed back. We tracked that down to the trailer battery. The 12 volt power wire (auxiliary) from the truck to the trailer was connected to the ignition side of the truck (only hot when truck ignition is on). We found that the power wire is wired to the trailer's battery to charge it when the trailer is connected to the truck. The charge wire from the trailer's battery was powering the truck which is what was causing it to not shut of once it was started. We moved the auxiliary power wire to the battery side (always hot). Note: The trailer has a power beaver tail and hydraulic jacks. 2) We installed a dedicated pressure sensor on the truck's brake airline for the brake controller. This allowed for the removal of the the brake controller wire from a brake relay in the fuse panel. 3) We now have marker lights, turn signals, 4-way lights, brake lights, and truck shuts off as it should. 4) Remaining Issue: The Prodigy P3 is showing Open Ground. It starts up green then goes to red with this warning when trailer is connected. If you pump the air brakes a number of times, it might turn green, then back to red with Open Ground Warning. We read the installation instructions and read your web site comments on open ground. It states an open ground is to the controller I believe. We ran several ground wires - to truck batteries and to frame of truck. The open ground does not go away. 5) Question - Is there possibility that the controller is bad? If not, What should we try next?

Jameson C.

3/24/2025

@Randall The open ground message on the P3 indicates that the ground wire of the controller (white wire) isn't connected properly to the negative post of the vehicle battery. I would go over that circuit and see if that helps.

Randy

3/29/2025

@Jameson. We have contacted the Mfr. They are sending a replacement unit. There should be no reason for an open ground given our setup at this point in time. We shall see if the replacement resolves the issue. Tks.