Nick,
Resistance values for the tach (grey) wire are 30-35 ohms for the old style and 35-40 ohms for the new style generator. There is an old service bulletin that warn of wire breakage in the older generators. In them, the grey wire is soldered to a resistor which is mounted on the stator and vibration causes a break at this resistor. Fix is to move this resistor outside the engine away from the stator.
Mag drop readings on the 582s are notoriously unreliable. The tach is reading six pulses per revolution normally, but when you switch half the system to ground during a mag check, the tach sometimes goes nuts on some engines. I have buddies who just ignore the tach and listen to the engine during mag checks.
Bill.
