MK2 Golf 4+e Clocks to Gti clocks with rev counter help?

Hi i have a 1988 golf mk2 4+e grandad spec. its a 1.6 with standard clocks with a time piece instead of a rev counter.
I have bought another set of clocks with a rev counter but im unsure how to fit and whether the rev counter will work? or do i need some rewiring and a sensor or something?