No Power on Blue Brake Output Wire on Reese Brake Controller

Updated 07/07/2025 | Published 08/31/2012

Question:

I dug out a compact controller, went to use it and found out im not getting power to the brakes from the blue wire. tested at the hitch, connections, and finally the blue wire at the unit. my old big monster controller works as it is supposed to, so, is my compact unit toast and look for another compact unit?

asked by: Nick

Expert Reply:

Assuming that the compact unit and the old unit use the same connection point, then you may be correct in saying that your compact unit is toast. Before pitching your compact unit, you may want to do some testing first.

The first thing that I would check is the connection between the blue wire from the brake controller and the brake output wire going to your 7-way connector. If you use a plug in style connector, then make sure there is not any corrosion, damaged wires or bent pins.

If you splice the wires together, then you will want to cut the blue wire about 6 inches back from the brake controller or before the connection point with the brake output wire and use a circuit tester like part # 3808 and test the blue wire on the brake controller for power when you activate the manual override.

If you do not have any power on the blue wire when you activate the manual override, then the brake controller is most likely the issue.

If the manual override works and you are not receiving brakes when you step on the brake pedal, then there may be a problem with the red wire, or the stop light switch wire. This wire should be connected to a wire coming from the stop light switch behind your brake pedal that only has power when the brake pedal is pressed. If this wire is connected properly and you still do not have power on the blue wire, then the brake controller is the problem and will need to be replaced.

expert reply by: John H

Michael S.

5/16/2025

I have a Reese brake controller that doesn't light up when plugged in to the universal controller plug. I have (battery voltage) 12V from black to white at all times on the universal plug and .35V on red to white at all times and 14.6V when the brake pedal is pressed. I've tried an additional reese controller and experience the same...(the controller doesn't power on) can you help me diagnose this? Is there a wiring issue in my 2007 suburban? I've completed the under hood connections and check every fuse I can think to check.

John H.

5/22/2025

@MichaelS Which Reese controller do you have?

Michael S.

7/2/2025

@JohnH I tried two different reese controllers. 8508211 and 8507111. Neither unit even light up when plugged in. It doesn't matter if the vehicle is running or not or if the trailer is connected or not. Did I randomly purchase two bad controllers or is there something in the vehicle that I need to chase down?

Jameson C.

7/2/2025

@MichaelS What's the vehicle and how are they plugged in? The black wire should have power and the white should have ground. Those are the first two circuits you need to verify.