Go the the auto parts store and pick up a good light probe trouble shooting tool. Has a tip like an ice pick.
Use that to find where the bad connection is. Just replacing parts only empties your wallet as you have already found out.
Start at the fuse block. Clip to a solid ground connection, then probe both sides of the fuse. Quite often, the fuse holder just gives up after a few years. If the fuse is good, follow the wire on its' path towards the lighting circuitry. Tedious, but the only way to get there.