I have a 72 Datsun 240Z with an Ignitor. I installed it as per the instructions. It runs great, but the tach will not work, any suggestions? Works great with points. I understand that the tach is a "current sensor" type, unlike most aftermarket units which operate off a signal from the negative side of the coil. I put the old coil back in (current coil is a Petronix), started the motor, tach went to 1,000 and then it dropped back to "0".