Troubleshooting 4-Pole Trailer Connector on 2001 Ford F150

Question:

my 2001 f150 crew cab has a 4pin trailer connection and has worked fine until just recently pulling my cargo trailer. Now the taillights as well as the running/marker lights have stopped, yet when I hook up the trailer 2 my 96 explorer everything works fine. I have checked,checked and rechecked every connection and continuity. Okay, now Im thinking it is a grounding issue on the truck side. Still nothing I have tried has worked and I am at my wits end. Any specific recommendations would be gratefully received.

asked by: John W

Expert Reply:

Let's start at the beginning. Since you've already successfully determined that the problems seems to be in the vehicle, and not the trailer wiring, let's begin with the trailer connector on your truck.

Use a circuit tester like part # PTW2993 and test the pins on the trailer connector as each taillight function on the truck is activated. The socket on the connector that's fed by the green wire should show signal with the right turn and the brake. The socket fed by the yellow wire should show power with the left turn and brake and socket fed by the brown wire should go hot with the running lights turned on.

If the trailer connector is OEM, there might be a blown fuse in the power distribution box, typically located under the hood. Check your owner's manual for which fuses protect which circuits and replace as needed. If you do find blown fuses, you'll want to find the short circuit that caused the fuse to blow and repair it, otherwise you'd better stock up on fuses. The short is most likely in the trailer wiring, so begin at the trailer connector and work your way back on each circuit. Look for pinched wires or loose connections. Check the ground point usually located on the trailer tongue, make sure its secure and not corroded. Make sure none of the wire insulation is worn or cracked.

If you don't find a bad fuse, and you have the factory installed 4-pole, trace the wiring from the 4-pole. Look for the point where the white wire grounds to the truck frame, and make sure the connection's tight and not corroded. The 4 pole harness usually plugs into a junction on the driver's side frame rail behind the rear wheel. Make sure the harness is securely plugged into this junction.

What I've mentioned above are what would be the most likely culprits. If you run through these items and still don't find the problem, get back with me and we'll look into it a bit further.

expert reply by: Mike L