Purchase a marine tach. It'll have a selector switch for number of poles. All the wires necessary are in the rubber plug sticking out of the control box...You can buy a harness to couple to it.
Ditto with Schematic. You can also go to www.teleflex.com, and copy the pdf manual for tachometers. It is a wealth of good information, and Teleflex seems to make 95% of the boat tachs too.
