Been reading about all your various symptoms. I have been fighting a taillight issue for 2 days. Only left turn worked -- No brake lights -- no running rear lights -- no flashers -- no backup lights. But driver side turn sig DID work. Changed all bulbs (were ONLY 25 yrs old) -- Ck'd bulb sockets (all ok) Ck'd fuses and pedal switch - both ok. Charted all progressive actions. Nothing made sense.
THEN thought back on what I might have caused when I took the bed off to replace a brake line in Sept. -- traced all movements I might have made that might've CAUSED the taillight issues. Looked the wire connections over and came to a ground at the frame near the trailer hitch lead. Took it loose - did a fair job cleaning the frame surface rust and reconnected it. Thought I had done a thourough job but still no change. Went back to that ground again -- took it loose -- stripped the wire casing back a couple inches and BINGO!!!!!!!! The wire was rotten ------------ Stripped the wire casing back real good
and got to good clean un-rotten wire -- took a FILE to the frame rail rust 'till I found bare metal re-attached the ground VERY WELL -----------'''-no more taillight problems'''. So if things get just too wierd - ck your grounds!