03 F350 7.3L
All lighting on the truck works fine.
Right now I have no running lights on the trailer when connected to the truck. They will go on with a lead to them from another source.


When connected to the truck the trailer has stop and turn as well as the brake control reading connected.


The truck has power at the trailer light fuse (38) and the fuse is good.


There is no running light power at the 7 pin end, the pin end when split apart or at the connector to it up by the spare tire.


While trying to search the problem, grounding has been mentioned. Unsure if it would apply here since it's only the running lights, however over the past winter the plug and bracket took a beating and I came across one green wire hanging out of the harness near the frame/bumper. Would that be a ground wire and/ or what is the next best thing to check between the 38 fuse and the rear connector at the spare tire? Thanks....

 

a green wire is usually always a ground wire.


I think you need to take you 7 pin plug apart and clean and connect the wires properly.

 

X2 Scott's suggestion

 

Thanks for the replies.


The pin connector is the two piece unit and it has been taken apart and a new pin connector has been put on. All the wires feeding the head appear to be secure and in place and the contacts also look very good. Everything worked fine in Feb., the last time it was used. Tried the whole wiggling and disconnecting reconnecting routine with both the plug into the head and head into it's connector.


Further checking there is no power to the running light post at the connector that connects the trailer plug wiring harness to the vehicle harness above the spare tire. The one you would unplug to replace the entire 7pin /4 pin connector harness. It appears there is no running light power going into the trailering harness itself. Trying to figure out the next best step as to where a problem might be between the 38 fuse and there. Guess I'll probably disconnect and feed the trailer harness separately and see if they work and go from there.


The green one that I mentioned is coming out of the harness up by the frame. If the green is usually a ground I'll drop the spare tire to see what I can do with it.
Thanks again....

 

Be sure to check the fuse with a meter or light, don't just look at it. I end up on service calls to change "good" fuses all the time. I check every fuse using my meter on the continuity setting or else both sides of fuse to ground with a light.

Steve

 

Using a light / swapped out fuse with another one in the panel that was known to be OK. Will triple check. I know that more times than not we end up missing something simple. Thanks for the advice, I'm sure I'll be needing more....

 

Just had the time to look at it some more.


Checked the fuse again by removing it and running current through it. Now positive it's fine


Ran current through the entire pigtail for the trailer hookup with the pin connector attached. Shows power to the lights.


Tried following the brown and white wire to the lower of three connectors that are on the inside of the frame in front of the fuel tank. Seems to show no power IF I'm checking the right one.


Now I'm into the engine compartment and the web of wires and connectors. I 'think' I have the right brown and white wire going into one of two small boxes on the wheel well. Took the cover off and it appears it has two relays. They both have FOAB 14B192AA on them. One also has 2086 A3 on it and the other has 2086 C3.


Would anyone know if these are related to the trailer lights or not. I haven't tried pulling them because I don't want to be disturbing anything more than I have to. Thanks again

 

Some of these are using the white as a ground as well. I take the white wire is connected to the 7 way plug?

 

You should be able to go here:


Owner Manuals | fleet.ford.com


Get the owners manual with fuse locations so you know which ones for your year.

 

You're right on the trailer plug itself, the white is ground at the plug. Have used it as a test ground. Appears to be fine.


I have the owners manual with the fuse/relay info however it doesn't indicate what the two separate boxes with relays under the hood (on the wheel well) service. I appreciate the link just the same


The brown and white appears to be the trailer running light wire. If it's the only brown/ white stripe wire in the truck it appears to be entering the relay box I mentioned before. The back will come off the box and expose the wires, checking the brown wire with a ground light, no light but the relay clicks.


Almost at the point where I might just splice in at the back and take my chances but I'm a little concerned about the wire size leading to the tag/ tail lights and or the truck light fuse being able to handle the running lights on a 32' fifth wheel.

 

Just a follow up.

Kinda solved the issue. May be just as well.Triple checked the trailer itself. Had another set of eyes go through all the steps with the truck and he was unable to find out for sure where the trailer running light issue is.

While double checking the connector by the fuel tank he stumbled across a corroded blue wire for the trailer brakes. Was able to correct that problem before it became a big problem.

I think the issue with the lights may lie in that connector as well. The fuel gauge runs through it and it has acted up on occasion and did so again as we disturbed it. Rather than open up a can of worms by disturbing a bunch of wires for running lights we addressed the brake wire, secured and buttoned up the connector and tapped off the truck at the rear harness for the running lights.

Thanks for all the suggestions. Not saying the problem is fixed, just saying this is where we found a problem. Thanks again.

 

Thanks for reporting back.


Maybe someday you will pull into those wires and get them all fixed up.

 

Fwiw that green wire that was spoke of by the frame / spare tire area is a stubbed out brake light only wire to he used for a third brake light on a canopy.

Green wires are rarely if ever used as grounds on 12v wiring.

Sounds like you have it working for now, let us know,the permanent fix.
Joe

 

Thanks for the info on the green wire.

Just took the trailer from the Mass/NH border to SC. Ran over night on the way back. Lights held up fine. If I find the right solution I'll be sure to pass it along.