Rev counter / tachograph mod

Hi. Does anyone know if the standard tacho can be modified to take a digital signal from an aftermarket ECU?

Thanks
Andy

possibly, depending on how its wired up.

start here:
VW Mk1 Golf Tacho Modification - Autosport Labs

see if you can find the SAK chip mentioned or similar, bypass all the signal processing and you should be good to go

or alternatively you can get tach adaptors form the likes of James E Looms or Chris Bellman on facebook, which are proven to be reliable well made units