So we were on our way home from the race track Saturday night. We got pulled over from the Indiana State Police for not having any trailer lights. We have brake lights, turn signals, hazards....just no running lights. I checked for corrosion at the plug and it had a little on it but filed it and still nothing...
Using a test light I checked our truck side...all works on the 7 pin except the running lights...I went to the next junction in the harness to the next plug in...all works except the running lights.
I obviously checked all fuses under the drivers side dash area...and found nothing...even pulled every fuse to see if there was an unlabled fuse blown...found my cigarette lighter was blown...didnt know that one!
My question is when I did searches online and on this forum for similar issues people were talking about trailer relays or another fuse box...does this apply to an 03 f250? Everything I found was on an older truck or the F150.
Also if there is anyone that has had this issue how was it fixed...I am not a whiz when it comes to tracing wiring issues and cant get much further than I got...next step is dropping the spare to see whats behind it.
2002-2004 trucks don't have a Power Distribution Box under the hood like previous and later trucks do. All the fuses are in the Central Junction Box, except for the PCM power fuse and some relays, which are in small auxiliary boxes.
To the OP, I would look up in your owner's manual and find the right fuse, then make sure you're checking with a continuity meter. If that doesn't work, find the relay and see what it's condition is.
I'm stuck! I'm trying to solve a similar problem, and get my trailer ready for camping in two weeks.
2002 Ford F250 7.3 crew
Checked out the trailer wiring by connecting a battery charger to each of the appropriate wires in the tow cable. Brakes, turn signal and running lights all lit up just fine.
Now turned my attention to the truck. Put a 12 volt probe on each connector contacts. turn signal (pin 5 & 6), brakes (pin 2), 12 V aux (pin 4), etc.. all work fine when I probe the connector on the back of the truck. However, there was no power on pin 3 for the running lights.
All fuses are good: Checked fuse 38 ("Trailer tow park lamps and backup lamps"), fuse 115 ("trailer tow battery charge") I'm thinking of buying a new relay 305 ("trailer tow battery charge relay") for ~$16 just to try something. I did have to replace fuse 115 a couple months ago when I first pulled the trailer out of storage. Also was having intermittent brakes, but found that one of the ground wires wasn't making good contact, but that's now fixed.
One thing that's odd is that I probed the socket for fuse 38, and it always has 12 volts, even when the lights are off.
How can I test the relay? The owners manual mentions a couple trailer relays: relay #305, but it's called the "trailer tow battery charge relay" Is this the one?
Also #6 the fuse panel is the "trailer tow turn/stop relay", but this doesn't sound like the one you're referring to either...
I look forward to your reply!
In the mean time, I'm going to try to find the schematic today and try to locate another relay in the circuit. From other posts I see that there is a chance that the relay you're referring to is embedded in the fuse box and isn't serviceable. Sure looking forward to testing it somehow.
PS: What does "CBJ" stand for? ("Circuit Junction Box"?) I assume this is what's also referred to as the fuse panel?
I had a very similar problem that I fought for quite some time. Ended up being a fuse (can't remember which one right now). It required more than an eyeball test. I had to test them all with a multimeter. I found that the fuse was not making good contact in its socket. It was not burned out just not making good contact. I put a little twist in the fuse and it has been fine for nearly 2 years now. Pull your multimeter out and test every fuse with it in the socket. That will allow you to wiggle them around and make sure they are all making good contact.