This may or may not be a good strategy
1....You want to find out that there is or is not (should not be) voltage drop between the ballast resistor ignition switch feed, through the harness, switch, bulkhead, all the way back to the battery
2.....Ballast voltage will vary A LOT depending on whether idling slow or engine off, etc, the type of coil you are running, and just plain variations over the years
So........
To check for voltage drop, with engine off, turn key to "run." Measure voltage between battery POS post and the keyswitch side of the ballast. You should have a VERY low reading, the lower the better. More than about .3V (3/10 of one volt) means there is voltage drop in there
2....Check coil+ voltage both with key on / engine stopped. and engine running at low idle.
Check again, rev engine up to simulate "medium cruise" RPM IE as if you were cruising down the street at 40-45 mph
Here, battery should read nominally 14V (13.8---14.2 if warmed up) and coil will read 10--12V +/- again, depending on the coil
