- Mar 9, 2016
I've searched these forums and many others but can't find the info I need. I have a 1969 Mercury 650 Thunderbolt 4cyl. And the matching tachometer. I've just ordered the wiring harness that plugs into the Mercontrol but the back of the tach is no longer legible as far as the hookup. It is a 3 wire setup. Anyone have experience with these old tachs who can shed some light on the proper hookup? Thanks.