I've got an issue that is stumping most everyone.

Look at your relay wiring diagram and see if there are relays and possibly fuses that put these two functions close to each other. Maybe a frayed wire is touching something just right so that when you energize that left turn signal circuit, it's arcing or shorting over to the wiring for the shift position sensor or something like that. Same could also be happening in a bundle of wires from the main harness where there are tons of wires bundled together. Wires age, connections are spliced, things happen.

 

I looked at the wiring diagram and an "off the wall" test would be to remove the 10 amp Guage fuse in the fuse/relay box by your left knee. This fuse powers up a quite a few circuits in the combination fuse relay. This combination fuse relay box has a pretty complicated internal circuitry, pluse it is a free simple test.

 

OP Status?

 

Don't know but does Toyota use flashers that control the lights near the fuses.Had an old truck n had to replace from time to time.

 

These electrical problems can be a real pain to track down but there have been lots of good suggestions so far. Start at the battery, clean terminals, good cables, good ground, then isolate circuits by pulling fuses, and working through one by one. Yuck!!!

 

Sounds like a short to power somewhere in one of the harnesses.