I've had all the symptoms you're talking about, and it was always a ground issue.
Yours may be different, but on mine you take all of the screws that hold the dash in place, and carefully pull it out toward the drivers seat, being careful not to disconnect anything. Up against the front bulkhead there's a silver buss bar. That's all of the ground connections. Using a screwdriver, and some contact cleaner, you loosen the connections a little, spray them, and tighten them down real tight.
You've got to find out where your buss ground bar is. Mine is on the front bulkhead up under the dash. Yours may be somewhere else.
Jim Sanderson
Canada, eh?