Before I go tearing off into this. I have a 1998 Ford F-150 4x4 with 5.4L and factory tow package. I plugged in my trailer and had no lights. No brake lights, no turn signals, no tail lights, nothing. I checked at the 8 pin plug on the back of the truck and the ground reads to ground. 12V+ reads twelve volts, but all other pins read zero volts even though all the lights work on the truck. I pulled the 8 pin connector apart hoping that it was just corrosion inside of it. There was some so I cleaned everything up and put it all back together but the symptoms remain. Is there another connector further up the frame that I need to check? Set of relays?

I checked my manual but it does not have a wiring harness schematic that shows a trailer wiring harness.

Any help or ideas will be appreciated.

 

Follow the link in my signature and download the 1997 owner's manual. The fuses for the trailer package are in it, but not in the 98 manual.

There is a separate relay box under the hood next to the main fusebox. The separate box isn't in the owners manuals, but you can check out this photo of my old 97 to identify relays. Trailer towing package relay locations - Page 2 - F150online Forums

 

If the fuses are good, follow the wires out of the back of your plug, it should lead you to a big T connecter mounted to the body, this is where the trailer harness is spliced into the system. It will have plug ins on each end of the T. You can get a replacement from Ford or most part stores.