I've had nothing but trouble getting my trailer brakes working and finally straightened it out friday night. Everything worked. Running lights, brake lights, signals, electric brakes. All checked out great. Saturday I took the trailer on it's first job. I worked until dark and no running lights on the trailer. All other lights work on the truck. I don't seem to be getting power to the green wire on the 7 prong (or 4 for that matter) plug.
Are the trucks running light on the same run as the trailer running lights.
This is 2004 F15 Heritage standard cab. I've looked at the fuse layout and nothing seems to be just for the trailer running lights.

 

I wonder if you have the same problem I had on my 98 f150 with the trailer tow package. On mine, the running lights and brake/ stop lights on the box worked fine but the trailer tow wiring had no power. Open your hood and look at the power distribution box on the left fenderwell. Don't open it, just look at it and then look backward slowly tward the firewall. Is there a smaller box just behind the power distribution box that has a relay in it? Now look behind that box even closer to the firewall. Is there another box, about 1 inch by 3 inches with tape around it? Peel the tape off of this box and open it. Is there any fuses in it? Probly one to be exact. Take note which slot it came from and pull it. Is it blown? If yours is the same as my 98 this is the fuse for the trailer tow pakage and its probly blown. This box is not mentioned in the owners manual, and if you didn't know it was there you wouldn't even see it. My box had a spot for 6 fuses but only one was installed and it was the one for the trailer lights. It was blown and replacing it made my day sunny and all my problems went away........ until my wife discovered I had it fixed and was now availible for other honeydews.


hope this helps..... MrMopar

 

In the fuse box on the left wheel well fuse #10 (20 amp) feeds the trailer running light relay R201 (in the auxiliary box- if yours is so equipped). Make sure both the fuse and the relay are there and working. Our relay wasn't installed. Maybe this will help.