I have a 2003 F-350, 7.3L Powerstroke. I recently bought a new RV. The running lights work fine as well as the charging, brake lights, turn signals, trailer brakes. However, after a few hours, the running lights quit working. Then, after a few hours of being shutdown, the running lights work again. I suspect that I have a relay that is causing the problem, but, I don't know where it is located. Can anyone help me on this?

Thanks in advance.

 

If you look at the Central Junction Box, (Fuse/relay panel) the relay is located in there.
According to my info the relay is not serviceable and the CJB may need to be replaced.

Sometimes a poor connection at the CJB can cause the problem you are seeing. It's a dog to get to , but worth the time to check it out. Make sure all the plugs are clean and no possible corrosion.
If the windshield has ever been replaced , they have been known to leak after replacement and that could have a bearing on the problem.

 

Hanky,
Thanks for the response. Where will I find the CJB? I have read some posts that indicate that it is under the dash behind the radio. But, I have also seen some diagrams that indicate it is in the engine compartment on the firewall. So, where do I look?
Thanks

 

Trailer tow battery charge is the only 'trailer relay' that is a replaceable relay in the CJB. CJB is located under the left side of the instrument panel and laid out as Hanky mentioned as far fuses, and as a non serviceable trailer lighting relay that's integrated into the CJB..

At the times it acts up, check both the 7 and 4 pin trailer connectors for running light voltage. Check the #38 fuse (both legs) in the CJB. If not a fuse/fuse connection problem, then possibly a CJB connector issue like Hanky stated. If none of the above,,, you can always wire in a fused stand alone relay wired to trigger off the H/L switch and splice into the trailer connector/running lamp circuit rather than spend the coin for a replacement panel..

The CJB has multiple connectors on the backside. The '16 pin connector' will have circuit for the trailer running lights. If the fuse/fuse connections are good, and the BN/WH wire coming out of the connector proves to not have a lamp output voltage, the relay is probably done..