Tach replacement

[BayouRunner]

Ok...I wanna say I've asked this before, but it's been awhile since I've been on the site, and am to lazy right now to look for it...so I'ma get input and advice again, if y'all don't mind.

I took out a bum tach...3 post..on a 150 Performance Plus with a 1990 Mercury 115. I was given a CAT tach, which supposedly came out of, or is used in Caterpillar brand equipment. My questions are: 1. If this is a Caterpillar equipment tach, can it be used in my boat? 2. The old tach was a 3 post, and the one given to me is a 2 post. I know which is my ground and power wire, there were 2 other wires that didn't go to any of the instruments, so I'ma assume there for the sending unit from the engine??? Does it matter which one goes where? I'ma assume, again, 1 would go to power and 1 to ground?? Or do I have to have a 3 post tach??

 

[Barnacle_Bill]

Re: Tach replacement

You have to use a marine outboard tach.

 

[BayouRunner]

Re: Tach replacement

Thnx...it was free, so I'll be thankful I didn't BUY it, then find out I can't use it.

 

[Silvertip]

Re: Tach replacement

You said the CAT tach is a two post, yet you say there are two other wires. That makes four connections. If that tach came from a diesel engine it either has a mechanical drive or a tach sender. A mechanical drive would have a threaded deal on the back that would accept a cable that resembles the speedometer cable on a car. But it would have to be an older car since car speedometers have been electrical for years. But this is all moot because the tach would very likely not be calibrated for the speeds that a two stroke motor sees. That little detail, plus the calibration issue makes it pretty well useless on your boat. Diesels are pretty well out of breath at 3600 RPM (unless you happen to have an Audi racing diesel).