If it's the 96+, it can the "multi-function switch." I had no brake lights and chased it down to brake light switch, so I changed that and nothing. Then I changed the multi function switch. The wiper motor wasn't working before, but after the multi-function switch swap it started working. Cruise also works, but never checked before. In the end, I undid the wiring and found out I was missing the big, 40A fuse and had some wires hacked away. Bought the truck last year.
My suspicion is that the previous owner had one of the parts that I changed and tried to Jerry-rig the brake lights...
I'm not sure if this is the same as someotherguy is saying and I hope this helps.
A voltmeter is very handy to have for checking circuits, along with a basic test light. Wiring diagrams are also extremely valuable to have. Make sure to get the right ones, ie, 88-95, 96-00