Porsche 911 930 Turbo rev counter issues

[howardstorey]

Wonder if anyone has seen the strange performance from the rev counter on a 1987 930 Model ?
works great most of the time then for no reason goes into a spasm of not working over working (showing 5K at tick over) then it is fine again seems to be affected by the indicators taking voltage and the lights I have check all the normal stuff battery terminals etc, and done a charging check seems ok at 13v at idle 14v at 4000 rpm ? ,
any ideas ?
thanks H,

[RVVUNM]

That happend to me, unfortunatly you will need to repurb or replace your altenator.

[ceven47]

Quite common, just a voltage regulator.

[jakebarrell]

Yes, I agree, it is mostly because of the voltage regulator.