Re: 1985 Merc 9.8 tach hookup
Check your controller for a tacho connection socket, some have that facility. if so you can perminatly fit it. If not then connect one tacho lead to the primary (negative (-)) terminal of any one coil. Connect the other lead to a good ground on the powerhead.
Timing light is connected to the No 1 spark plug, dont know if you can use a car one, your linning up timmimng marks, so cant be that different.
Youll'e need a dial indicator to find TDC, and a water tank for the engine.
Personely Id take it to a marina than buy all the tools and stuff.