Fluctuating neg. to ground on ignition coil
Finally got time to do some measurements:
The ignition coil is getting between 7 and 7.7 volts at + when running at idle, it's marked with 12 Volt, I have yet to remove the ignition coil to see more text on it.
This might not even be a problem. Did you try increasing RPM up to "high cruise" maybe blipping it very high and see what is and at about what RPM you get maximum voltage, and what that voltage is?
The thing is, CURRENT affects this, as well as the alternator (regulator) affecting charging voltage. Current, more of, coil heating, ballast heating, and charging system voltage variation causes more or less voltage drop through the system and through the resistor.
At quite low idle, the system charging voltage may NOT run at 14. At higher RPM and due to the typical voltage drop in harness, the battery may see HIGHER than 14.
The coils VARY and as old as these girls are may have CHANGED value as well as having been replaced with a somewhat different coil
YOU CAN NOT TRUST low value resistance measurements
YOU CAN NOT figure current based on COLD resistance measurements, because BOTH the ballast AND the coils CHANGE RESISTANCE when heated
(You cannot even do that with lamps because the cold resistance of a filament is much lower cold than when operating and heated)
It might be the coil is a little "hotter" than original, that is, more current
It might be the ballast has a little different curve than the original AND BE SMALLER RESISTANCE WIRE
If you are starting to get the idea that there are "all sorts" over possible variables......you are right!!!!
If you are insistant, put the thing on a scope and see what the coil reserve voltage is. Measure from ECU case (and regulator case) to battery NEG and make sure there is no voltage difference at ground.
