55 hp mariner marathon rev counter issues

Hello to all,and sorry if this is a double post.
Got two 55 hp 3 cylinder two stroke Mariner engines,manual start.
Can I fit rev counters and how do I connect them up. Or do I need to change something,or even the charging circuit which I believe is not in,as this motors is manual start with rope.
Thank You

The grey wire in the harness connector is the tach signal wire. If I remember correctly and if you are able to hook up a harness to your plug, grey is the tach signal, purple is the 12v switched power and black is a ground. Or just get a ground from something else. If all you're doing is hooking up a tach, that's all you really need to know.

Alternatively, you could use something like a "tiny tach" to just keep track of hours and have a small digital tach. Very simple and straight forward to install, although not as accurate as a "real tach", they are good enough.

Ah,
Thank you so much. Will get to it over the weekend and give feedback.