Thank you all for your input.I did connect tach to the - side of the coil with the green signal wire from the tach but the tach will not move.This is the 2nd tach,I sent back the first one because it only moved off zero a small amount.Wondering if I need a tach adapter?Acton says it needs 5 volts from the coil,I have about 6 volts.Any ideas???Pertronics say call Acton.This is a Sun Pro II mini model CP7904.Nice little tach if I can get it to work.Plan on installing it were the stock nonworking clock was removed.