Tachometer for Farymann A30?

Greetings, I installed a new instrument panel this week with a new bilge pump switch and planned to install a new tachometer for my farymann. The old tach was rusted up and not working and the old instrument panel had a bad run in with my foot one day and ended up with a big whole in it. oops... I went to wire the new tach. and found that the send wire wasn't connected to anything on the alternator (the plot thickens). I can't tell from looking at the alternator which to connect the send to - nothing is marked "AC". It is a Motorola alternator (not sure how old) and I don't know if it has a tach pick-up or not, and if it does, how do I distinguish which one it is? There are four wires connected to the alt. at this time... non of which go to the old tachometer. Hints/tips? If the alternator doesn't have a tach pick up, I need to install a magnetic pick up, right? I have been using my boat for a year with no instruments for the engine. The guy I bought it from said, "If water is coming out the back and it's still running, I assume everything is fine". Maybe I'm not so optimistic... Matt 1974 Cal 2-27 Je T'aime