Vauxhall cavalier rev counter intermittent?

The rev counter on my 1992 Vauxhall Cavalier automatic sometimes reads ok other times reads high. where is the pulse taken from to work it?
Brian, June 2005


done
is the revs rising then falling if so a 1mm hole in the throttle body butterfly valve will sort it

jamie menzies, December 2005
I AM NOT 100 PERCENT SURE BUT I THINK IT MAY BE ATTACHED WITH A WIRE TO THE ALTERNATOR.REMOVE WIRE AND CLEAN IT UP THEN REPLACE .POSSIBLY!

IAN, June 2005
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