Originally Posted by
warriorm
You should have a second fuse box under the hood. That's where most of the trailer stuff happens. My '99 E-350 has one, as does my '08 F250. I'm guessing your '03 will have one as well. Good luck.
I don't think so Warrior. I own an 02 V10 and work a 02 7.3L and neither of them have underhood boxes. The older 2000 that I work with does, but both 02s have it under the dash.
If I remember correctly there are 3 or 4 main fuses that correspond to trailer lighting. One of them was a running light fuse.