TOPIC: Will this tach work?

Here's the wiring diagram for a tachometer I came across. It can be set for 4,6, or 8 cylinders. Can this be wired to work with a 1967 Merc Thunderbolt 500?

Yesterday I just wired the same tach to my 1966 Evinrude. Everybody was telling me I needed a $90 tach.

Works fine, haven't had it on the water yet but it reads about right in the driveway. Use the 8 cylinder setting. (That is a 4 cyl 2-stroke right? I don't know my Mercurys).

Installation is simple.

OK,Thanks! Why wouldn't I use the 4 cylinder setting?

Assuming it's a 2 stroke, it fires twice as often as a 4 stroke. The distributer in a 4 cylinder 2-stroke fires the same number of times as an 8 cylinder 4-stroke for a given number of revolutions.

That's also why 2-stroke motors can produce higher horse power in a smaller motor, they fire every revolution whereas a 4-stroke fires every other revolution.

It is a 2 stroke- Got it. Thanks.

OK, Here's what I have- 1967 Thunderbolt 500. The accessories (i.e instrument lighting) use a separate battery from the starter battery. Must I use the starter battery for all the connections here? Where does the green wire connect? Appreciate the help.

Do yourself a favor. get a new teleflex tach that works off of the alternator.$ 50.00 should get one.easy to hook up.