Troubleshooting a Tekonsha P3 Brake Controller that Reads Trailer Not Connected

Updated 04/30/2020 | Published 09/28/2014

Products Featured in This Question

Tekonsha Prodigy P3 Trailer Brake Controller - 1 to 4 Axles - Proportional

(6472)

$170.94

Hook Probe Circuit Tester

(58)

$12.00

Question:

Hello, I can not get my new Tekonsha P3 brake controller to recognize the trailer connection. I purchased the controller and the 2005 F150 specific wiring harness. It always says trailer not connected. I have visually inspected almost all of the wiring, truck and trailer. The lights all work correctly to include brake lights but no trailer brakes. I have also tried checking the wires coming out of the back of the P3. Black was 12v, red is brake lights, white is ground, but blue does nothing. I know blue is the trailer brakes but I get no signal or output when pressing the brake pedal or sliding the manual override on the controller it just clicks and flashes red no connection. I have made sure the fuse for the trailer brakes is good but still no signal?? I have no idea what to even check next. Please let me know what you think. Thank you!

asked by: Dustin

Expert Reply:

If you sever the blue wire leaving the P3 controller part # 90195 leaving enough room to reconnect it and test the end of the wire leaving the controller with a circuit tester like part # PTW2993 you should see voltage when you slide the manual override lever. If not, then the brake controller is bad.

If you see voltage there instead then the problem is somewhere on the brake output circuit of your vehicle or trailer. Corrosion on the trailer connector typically causes this problem. If cleaning the connector on your trailer and on your tow vehicle does not fix the problem you will need to inspect the condition of the brake output circuit on both your trailer and on your tow vehicle looking for any obvious signs or shorts like cut or exposed wire and fix as necessary.

I attached an FAQ on troubleshooting brake controller installs for you to check out as well.

expert reply by: Jameson C

Chris

4/27/2020

I have the break controller Hooke up with the factory harness that you guys offer. Once the controller gets to 6 volts it shows that there is an open ground . I have by passed that with a separate ground and power lead but still get have the same issue when i apply the breaks. The controller is. Less than a year old could that be bad?

Chris R.

4/29/2020

A bad controller is possible but unlikely. Since you know the controller's ground is good, I would inspect both the vehicle's and trailer's 7-Way connector. Visually inspect both to check for any corrosion or debris that might be built up around/inside the pins, cleaning out as needed. Let me know if this doesn't help and we can go from there.

Chris T.

4/29/2020

Both. Trailers are new And both plugs on the truck are new. The truck is a 1998.5. Dodge 2500. In one of your install videos. It makes reference. To if the plugs are not a factory. Plug. There might be something else I need to do to make them work but does not say what? The controller. Recognizes the trailers all the lights turn signals and break lights work. But when you ask for a lot of break. It goes to broken ground no breaks. Is there I a difference between. The wire harness that you guys sell For the 1998. And 99.

Chris R.

4/30/2020

The truck is recognizing the new brake controller so you shouldn't need anything else done (the video was likely talking about taking the truck up to a dealer to have the computer flashed). If I understand correctly I believe you said the same issue is happening on two different trailers? If that's the case then we at least know the problem is somewhere on the truck. Does the problem occur both when pressing on the brake pedal and when using the manual override? If it's just with the brake pedal the brake switch on the truck itself could be going bad, which isn't terribly uncommon on older trucks.