A new harness is probably a wise bet. After chasing gremlins on my '84, I finally just pulled everything out and installed the large Painless harness. 40-some-year-old electrical components don't improve with age. It was worth it to know I wouldn't have to mess with the wiring again.
I used the Painless harness with 27 circuits in my '84 K20. Figured it couldn't hurt to have a few extra circuits available. Also used their premium Aramid fiber wire wrap package to try to bulletproof it a bit. It was a simple (albeit time-consuming) job. The Painless installation manual is...
One minor downside of farm living is that small animals try to get inside of anything they can. It's not unusual in the spring to have to remove Carolina Wren nests from the intake manifolds of trucks and tractors. Then there's rodents.
One cold morning recently the dog and I loaded into our...
Agreed. I meant the lever, not the switch itself. Sorry for any confusion.
But that still apparently leaves the OP with having to pull the steering wheel.
Unless there's some secret method I don't know about, you're going to have to pull the steering wheel and the turn signal switch to get at the high beam switch (which on my '84 is also the wiper switch). Might also have to drop the steering column in order to be able to fish the wires through...
You've got several excellent opinions here.
Look hard at the #$%&*!! proportioning valve. I had one give me fits and produce the same symptoms you're having.