My 1998 Toyota Camry (with 208,000+ miles) has a right turn signal indicator that blinks very fast. Neither front or back bulbs are burned out, but the left headlamp does not work unless on bright. The fast blinks occur only when I am running the headlamps. I just replaced the headlamp a few months ago, and this will be the third replacement in 5 years. The dome light inside the car also does not work. Occasionally the driver side window refuses to go up. If I stop the car, restart it (like a balky computer), it usually works. (I avoid drive-throughs.) Are all these symptoms likely the result of an electrical problem in the car, or are the problems likely unrelated?
About the turn signal and headlamp - Check for a bad ground to the headlight/signal light assembly.
I guess you avoid drive through car washes. Check or clean the ends of the ground wire that is usually found near the alternator and connects to the fender. Take the fender end off and wire brush the end or just scrape it and reconnect. You want a good connection there. Strange things can happen without a good ground. Don’t lose that screw or bolt. If you do, don’t start the car until you get reconnected or your alternator might quit.
I agree with the others thought on a bad ground lead causing this trouble. The higher current needed by the headlights is causing a voltage drop across the bad ground connection so the blinkers can’t get enough current through them when the headlights are on. Check and clean the grounding leads between the negative battery post and the chassis ground.