Troubleshooting Trailer Connector on 1998 Ford F150 With No Output on Running Light Circuit  

Question:

Expert Reply:

According to the owner's manual I found online, there are two fuse locations you can check, assuming that the 4 pole trailer connector you're speaking of is factory installed. In the passenger compartment fuse box located under the dash to the left of the brake pedal, check the fuse in location # 18 and replace if necessary.

In the power distribution box under the hood, the fuse in the # 1 position controls the trailer running light circuits, check and replace if needed.

If you find a blown fuse and replace it, before plugging in the trailer you'll want to find the short in the trailer wiring that caused the fuse to blow. Examine the running lamp circuit on the trailer, beginning at the trailer connector. Make sure the connector itself isn't corroded or damaged. The running light circuit is usually a brown wire, which you'll want to trace all the way back to the trailer taillights. Look for places where the wire is pinched, or for cracked or worn insulation that would allow the copper wire to short out on the trailer frame. Check the bulb sockets to make sure they aren't corroded. Make sure all connections are secure. Repair any cracked wire and replace the trailer lamps if the sockets are overly corroded.

If the fuses are fine, you might be better off simply abandoning the factory 4-pole connector and installing a new one using part # 118344 which would plug inline between the taillight assemblies and the vehicle's taillight wiring harnesses.

I'll link you to our trailer wiring troubleshooting FAQ article.

expert reply by: Mike L

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