Troubleshooting Trailer Wiring With 2008 Ford F-450

Updated 04/25/2019 | Published 04/23/2019

Question:

2008 f450 6.4 diesel king ranch dually. We are having some wiring issues. No power in our running lights on our trailer until we turn the keys on. They should turn on with the light switch, not with the key switch. Once they are on, they are lit all the time. They don’t turn off with light switch. Only with the key. Advice?

asked by: Jan T

Expert Reply:

For the issue with your running lights test the connector on your vehicle with Circuit Tester # PTW2979 or a similar one after disconnecting it from your trailer.

If the signals going to your harness are okay, you'll need to test the signals coming out of the harness, and if they are correct then your issue is likely going to be with the trailer side wiring. You will also want to check both your vehicle and trailer connectors for corrosion, which can be green or white in color. A build-up of corrosion can interfere with the signals getting through the connectors so if it is present you will need to either replace the plug or clean the corrosion.

You'll also need to make sure your grounds are attached to bare metal surfaces and free of any paint, dirt or corrosion. Finally, check your wiring thoroughly to ensure there are none that are crimped, broken or otherwise damaged.

I have added links to a pair of help articles on trailer wiring, including a troubleshooting guide which I highly recommend taking a look at.

expert reply by: Kyle S