How to Test Vehicles Brake Controller Wiring to Determine Wiring Function

Updated 05/29/2018 | Published 05/25/2018

Question:

Okay, so my truck only has four wires but does have the 4 way plug and 7 way. Okay so the question is the plug under the dash has a red, blue, black, and green. On the reese tow controller I bought has red, blue, black, and white. Which wires go where cause right now I have color to color and white to the green and it keeps blowing the fuse. Please help. Its a 2005 Ford f150 with a 5.4

asked by: Jesse S

Expert Reply:

If the wiring you found is correct for installing a brake controller it's not the standard colors we are aware of for a Ford truck. So what you'll need to do is use a circuit tester like part # PTW2993 to test the wires for function and then wire accordingly to the Reese brake controller. Which the controller wire colors are white for ground, black for 12 volt power, blue for brake output, and red for brake light circuit.

The 12 volt circuit will be one that has power all the time, the stoplight circuit will be the one with power only when the brakes are applied.

Ground the tester to the constant 12-volt power wire, then probe the remaining two wires. The wire that lights the tester will be the ground, the other will be the brake output circuit.

expert reply by: Jameson C