I have an old 1960 runabout that came with an old (don't know the year) airguide tachometer. The previous owner used it with his late 1960's merc. I now have a 1990 Yamaha 2 stroke on the boat and I cannot get the tach to work. The tach has two wires to it which I was told to hook up to the tach lead and the ground. When I do this the needle jumps quickly back and forth. As I rev up the motor it jumps higher on the scale. I have read some of the previous posts about pulses and poles and magnetos versus coils, As far as I can tell there is no way to change the pole setting on the tach. I was also told that it may be a DC versus AC signal problem. Is there any way I can get this to work? I have a newer Yamaha tach that came with the motor, but I would really like to keep the old classic tach to match the boat. Thanks for your help.
