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Troubleshooting Trailer Running Lights Not Working When Towed By 2001 Ford Expedition


Trailer running lights. No trailer running lights on my 2001 Ford expedition.


Expert Reply:

The single most common cause for trailer running lights to not work is a bad ground connection. Since these lights remain on continuously (unlike brake lights or blinkers) they will demand more current. The issue arises when the ground connection is not solid enough to allow the full amount of power to pass through to the trailer lights.

So the first things to check are the main ground wires on both the Expedition's harness and on the trailer's harness.

Ground wires are most often white and their ring terminals need to be firmly attached to a clean bare metal surface. The existing grounding points may simply have become corroded. You can try sanding them off, protecting them with dielectric grease like # 11755 and then re-attaching the ground wire ring terminals.

If that does not correct the issue you can test the running light circuit pin on your trailer connector. On a 4-pole setup this will be the pin for the brown wire. On a 7-way setup the running light circuit is carried on the pin at the 11-o-clock position as you look at the vehicle socket (see the linked photo please). Use a circuit tester like # 40376 while a helper activate the lights on the Expedition. The pin for the trailer running lights should have the signal when you turn on the vehicle headlights.

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