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P3 Brake Control Shows No Trailer Connected Even with Trailer Connected to 2002 Ford F-150


I bought a tekonsha p3 and installed. When I hook up to a trailer that I know has good and working brakes, my brake box still says no trailer connection. Was wondering if you had any info on this? Would greatly appreciate it. The truck is a 2002 ford 150


Expert Reply:

A brake controller like the P3 # 90195 senses the brake magnets on the trailer when connected to the truck. It is possible that the blue wire (brake output wire from the controller to the trailer) is broken or missing somewhere so it cannot sense the trailer.

To test this adjust the controller to the highest setting. Then have someone sit in the truck cab and fully apply the manual override lever while you test the brake output pin in the 7-Way connector at the back of the truck using a circuit tester such as # 40376 or a meter like # PT89ZR.

If there is no power when you do this test then do the same test only check at the blue wire at the back of the controller. If you don't get power there either then there is a problem inside the controller and it will need to be replaced.

But if there is power at the back of the controller but not at the truck's trailer connector then the issue is likely a damaged wire somewhere between the controller and the connector at the back of the truck. Or you could run a new wire if you wanted to (if the wiring on the truck is difficult to access). You can use wire # 12-1-1 sold by the foot.

I have also included a couple of links on testing and troubleshooting brake controllers for you with additional information but I suspect it is just a bad or missing connection.

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