For the most money I can buy a factory wiring harness. I see LOTS of aftermarket tachs but with little or no info about what is necessary to wire them up. Would you go with an inexpensive tack [I read about Tiny Tachs] or a factory [$$] model. I believe my motor has an accessory plug connection, not sure how difficult it would be to 'wire into' it with aftermarket stuff. Anyone install a tach for their Merc 3 cyl 4 stroke motor? .