2009 Ford F-250 Super Duty Showing Trailer Wiring Fault

Updated 01/28/2020 | Published 01/25/2020

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Pollak Metal 7-Pole, RV-Style Trailer Socket - Vehicle End

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Digital Multimeter with 42" Long Test Leads - LED Display

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Question:

All functions on trailer when plugged into the truck work except electric brakes. I have plugged other trucks into my trailer and brakes work. i tested the power to the elecrtric brakes at the plug and the tester light is very dim even when the trailer brake controler is set at max gain 10.0 . I tested the other truck and when brakes are engaged the tester light is extreamly brite. Is the problem in the trailer brake controler or the wirering ?

asked by: Corey H

Expert Reply:

Your problem could result from even a slightly dirty, corroded or loose connector (or individual connector pin) anywhere from the dash all the way to the 7-way. Corrosion can sometimes appear as a green or white film (connectors do not have to look badly corroded to have issues). Even a small amount of oxidation on a connector could inhibit the signal transmission.

Carefully inspect all wiring, from the connector to your brake controller under the dash, all the way through to your 7-way at the rear.

You may want to start at the 7-way connector since this part is exposed to the elements. Use a multimeter (such as part # PT89ZR) to test the voltage output on the brake controller output pin, at the 5:00 position. Read the voltage from the pin. Now disconnect the connector harness from the vehicle wiring and re-test at the corresponding pin on the vehicle harness (the one with a blue brake signal wire). If you read a higher voltage on the harness than on the connector then you have a bad 7-way connector and can replace it with part # 42145. If the connector and harness show the same voltage then you need to continue checking the rest of the wiring.

A loose (white) ground wire anywhere in the wiring could also cause this problem; if the controller was hard-wired make sure the white ground wire is firmly attached to the battery negative terminal. Check for any wire with cracked insulation. Wires can develop wear spots in the insulation from the normal vibration that occurs during driving, especially if the insulation comes into contact with other parts of the vehicle.

Also check for any pinch points around the wires and re-route them away from suspension and exhaust components if any are nearby. Any badly damaged wire should be replaced and any worn spots should be securely sealed with electrical tape.

If this does not address your issue let me know and we can try more troubleshooting items. Included is a help article too.

expert reply by: Patrick R