The tachometer on my car (73 GT) won't register above 3,000 rpm even if I rev
the engine above that. The needle dances when I switch on the indicators or
hazards to the rhythm of the flasher unit(s). I measured current coming to the
unit with an analogue multimeter and it was as you described. I gave it a tap
with my hand but nothing changed. Would you say the gauge is at fault?
> OK, then you should have 12v on the green, ground on the black (a wiring tag
> secured under one of the knurled nuts that clamp the tach onto the dash) and
> the white/black should be switching between 12v and ground when the engine
> is running. Note that an analogue meter will display this last as about 6v
> and a digital meter may not display a settled reading at all. If you have
> an after-market electronic ignition system you may get different readings on
> the white/black, and this can be the cause of the tach not working anyway.
> If you have these readings on the back of the tach the wiring is OK and the
> tach itself is suspect. By the way, seeing as how the car has not run for a
> couple of years it could be stuck. Have you tried giving the tach a rap
> with your knuckle while the engine is running? If the needle bounces off
> the end stop but still does not register then the problem is possibly
> electrical inside the tach and not mechanical. If it stays on the end stop
> it could be well stuck.