Speaking of tach not working...

[Bob]

.... the tach on my 85 4000Q doesnt want to be so cooperative. Turn on
the key, it reads about 1200rpm (engine not running) Start the engine
and it goes up a little and stays there.  Engine rpm have NOTHING to do
with what that gauge does. To add to the confusion, every once in a
while it works just fine!
I took the gauge cluster out, cleaned every connection, replaced the
dead bulbs, put it back together, no change.  I thought I recall phil
mentioning something about this about a hundred years ago, but I couldnt
find it anywhere...
Bob