Troubleshooting Running Light Circuit on 7-way of 2010 Ford F350 Diesel

Question:

I have a 2010 F. 350. Diesel truck. My problem is I have no power to my tail/marker terminal on 7 way plug. Everything else works fine. Fuses look good. Any suggestions?

asked by: Randy

Expert Reply:

Which fuse box did you check? In addition to the box under the dash, there's also fuses located in the power distribution box under the hood. You'll want to check the fuses or relays in the following locations: 20, 21, 42 and 55. It's not always easy to determine if the fuse is blown by looking at it from the top. It's easier to tell if you can remove the fuse and give it a side view.

You'll also want to rule out the connector itself as being the problem. Unplug the wiring harness from the rear of the trailer connector and use a circuit tester like part # PTW2993 to probe the pins in the factory harness. When the vehicle running lamps are on, one of the pins should show power. If you find a pin with power on it, but no power on the running light pin when the 7-way is plugged back in, you've proven that the 7-way is damaged and should be replaced. The # HM40975 would be a good replacement.

If you can't find a hot pin on the harness when it's unplugged from the 7-way while the vehicle running lights are switched on, and all the fuses and relays were fine, then there's a wiring problem between the tow package and the trailer connector that will need to be tracked down.

expert reply by: Mike L