I had a 1959 boat with fins. Had the Airguide tach in it. Was a 2-pole tach and was connected to the 1976 75 hp short shaft engine. Somehow it worked just fine. I bought it that way and never had to hook it up, so don't know what goes to the two poles. Obviously, one is the signal. I do not believe that it had an adjustment screw on the back of the tach to set the # of alternator poles, but that was years ago..