I just bought a digital tach for my 1300 S 2003 model. Instructions say red wire to hot, black to ground, green to ign. I connected the green to one leg of the front coil. Tach worked but only shows half of the RPM. Like it shows 623 rpm's at idle,and I know it should be about 1000 rpm's . Any ideas. I am sure that some of you folks have installed one, and know how to make it work right, Thanks for any help.