I have a 1990 F-250 XLT Lariat RWD with a 7.5l and E4OD. My stepson borrowed my truck a while back. When he returned it he mentioned that the tail lamps and the dash lamps did not work. I did a little research on this site and narrowed the problem down to the headlamp switch. I dismounted the switch so I could look at the back of the connector, and BOOM two of the wires had backed out of the connector. I pushed the wires back in until they were fully seated and all my lights work. My thanks to everyone who contributes to this forum. It really makes chasing down annoying problems a LOT easier.

 

You were lucky, I had similar issues, because my switch connector melted.

 

Exactly!
Now would be a good time to invest into a headlamp relay upgrade.

Glad to see it wasn't damaged.

 

I am going to put it back together and let it be for now. I saw no signs of overheating.