Low Voltage at 7-Way Connector on 2005 Ford F-150 Using Prodigy P2 Trailer Brake Controller 90885  

Question:

Expert Reply:

It sounds as though you are using your Tekonsha Prodigy P2 Brake Controller # 90885 with a custom-fit harness like part # 3035-P to connect the controller itself to the factory brake control port under your dash.

The first troubleshooting step is to check that the controller output is correct before it travels through the vehicle wiring to your 7-way. Cut the blue wire a few inches from the connector at the back of the Prodigy. Apply your grounded circuit tester to the blue wire coming from the Prodigy and press the brake pedal. If you do not detect a full-strength brake output signal on the blue wire then you will need to check the other connections to the controller. (This could also indicate a damaged brake controller.)

First you can remove and inspect the harness that connects the Prodigy to the under-dash port. Look at the connector on each end for signs of bent or damaged pins or any corrosion or dirt (even very slight greenish or whitish discoloration can indicate corrosion that could interfere with the signal). If you have a volt meter you can test the harness itself for continuity on each of the four circuits. Clean or replace the harness as needed. You can next check the red wire to the controller. This wire carries the signal from the brake pedal switch that tells the controller to generate a brake signal for the trailer. You should detect a signal on the red wire only when the brake pedal is pressed.

If the controller is generating a full-strength braking signal on the blue wire (close to 12 volts) and the harness is good then you know the problem is somewhere in the vehicle wiring downstream of the controller and connection port. In this case reconnect the cut blue wire and securely tape it; and re-install the plug-and-play harness.

Next inspect your 7-way connector for signs of bent or damaged pins, corrosion or trapped dirt or moisture. Sometimes trapped road dirt or water can bridge two circuits, causing a short. Follow the wiring forward toward the OEM connector on the driver-side frame rail, usually between the back tires and the rear bumper. Please refer to the photo provided. Again, check that this connector is in good condition. You can use a circuit tester (like # PTW2993) to see if the brake signal is reaching the OEM connector by testing the blue wire that leads to it from the front of the vehicle. If there is a full-strength signal reaching this point you will need to replace the 7-way portion, using part # HM40975.

I have linked an installation video for this controller as well as an article concerning brake controller installation in a Ford truck. I have also included a brake controller troubleshooting article for reference.

expert reply by: Adam R

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