I have a 86.5 Toyota supra, and when I use the turn signal, the battery gauge needle jumps up and down. Other lights on the dash also flicker when the turn signals are on. This happens when the car is running, or the key is just in the on position.
Do other lights, like the dome light or head lights also change? I think not and if not then I would look for a poor ground to the instrument panel.
Do all the turn signal bulbs work properly?
yes
the headlights also makes the gauge move, the dome light doesn’t, but they are pretty small. When I turn on the emergency flashers, the battery gauge and the tachometer both jump around.
This ONLY happens when the turn signal stalk is used?
read above comments
I am a little confused. Let’s start over. Is the only problem the fact that lights and the gas gauge react to changing load on the system with the engine running or not?
I am suspecting a poor connection or a bad cable. Remove, clean and properly re-attach each end of each battery cable and cables to the alternator.
thats pretty much the problem, i will try that