Hello guys!

I got a sierra mk1 2.0 pinto engine.
The car didn't had rev counter when new, i bought some dials from a sierra mk2, i got all wires worked out and everything works except the rev counter, i know the 2 green wires that came from the plug of the dials are for the rev counter but where do i connect them? I know they sould be in the alternator but where? Which cable or terminal? Do i need to change the alternator?