> The tach on the '70 GT pegs when I crank the engine, and works fine when
> it starts. I've also noticed it pegs when I switch on the windshield
> wipers with the ignition on and engine not running.
I'm anxious to see if there are any hints on this. My '71 Midget does a
similar thing, though not consistently. Never noticed any connection to any
other circuit though (like your wiper problem). But sometimes it pegs just
turning on the switch, usually accompanied by a high-pitched squeal. I'm
guessing that the points happen to be in a closed position, so perhaps the
constant current flow is being seen as "infinite" RPM. A couple of times
when this has happened the tach would read around 3K too high - I'm guessing
some capacitor in the tach picked up a full charge and was sort of "biasing"
it. Another time it didn't work at all after starting. Most of the time it
seems fine though. Kind of strange.
I've been surprised that my tach works anyway. It didn't when I got the car,
so I opened it up and discovered a transistor that hadn't been properly
soldered to the circuit board and one lead had come loose. Resoldered it and
it pegged the needle first try, but after that worked nicely - was even very
close to being properly calibrated. So whenever it works, I'm happy. ;-)
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