Well, finally got my new tractormeter working with my 12 volt alternator. First bought an alternator from Bill at Howard Enterprises which had a tach drive:
http://www.ebay.com/itm/Tractor-GM-alternator-w-tach-drive-Massey-Ferguson-Allis-Chalmers-External-VR-/230892303945?_trksid=p2047675.m1850&_trkparms=aid%3D222001%26algo%3DSIC.CURRENT%26ao%3D1%26asc%3D11%26meid%3D4233480225765573162%26pid%3D100011%26prg%3D1005%26rk%3D1%26sd%3D330787489654%26
I bought a new Tractormeter and cable and hooked it up. Using a dwell meter the tach ran 25% higher RPM than engine was running. The pulley on the alternator was 3.20" diameter so I needed a 4.00" to reduce the alternator RPM buy 25%. I found a Powermaster 182 (4.00")aluminum racing pulley that fit perfectly. After replacing the pulley the tach is about as accurate as one can expect, maybe within 50 RPM's. I have the idle set around 700 RPM and the alternator still puts out over 13.5 volts. Bill at Howard was great to work with and definitely has a great product for those who want to do a 12v alternator conversion yet want to keep the original tach operational.
http://www.ebay.com/itm/Tractor-GM-alternator-w-tach-drive-Massey-Ferguson-Allis-Chalmers-External-VR-/230892303945?_trksid=p2047675.m1850&_trkparms=aid%3D222001%26algo%3DSIC.CURRENT%26ao%3D1%26asc%3D11%26meid%3D4233480225765573162%26pid%3D100011%26prg%3D1005%26rk%3D1%26sd%3D330787489654%26
I bought a new Tractormeter and cable and hooked it up. Using a dwell meter the tach ran 25% higher RPM than engine was running. The pulley on the alternator was 3.20" diameter so I needed a 4.00" to reduce the alternator RPM buy 25%. I found a Powermaster 182 (4.00")aluminum racing pulley that fit perfectly. After replacing the pulley the tach is about as accurate as one can expect, maybe within 50 RPM's. I have the idle set around 700 RPM and the alternator still puts out over 13.5 volts. Bill at Howard was great to work with and definitely has a great product for those who want to do a 12v alternator conversion yet want to keep the original tach operational.