1991 Chevy Cavalier Tail lights, dash lights and dome light

The brake lights work fine but tail lights and dash board light and dome light do not. I checked the fuse, and a 15 watt fuse was dead, I tried to replace it but couldn't put the new fuse in the slot I thought it came out of. I put it in another slot that accepted it, but I'm sure was one line over. Also horn does not work. I don't know it all of these are related - dash, dome, tail lights and horn? I know the tail light situation can be a lot more serious issue, wiring etc.
I would love to donate money but my computer is infected with trojans (long story) which can only be solved by reinstalling operating system.