Found this online while searching vintage coil load testing machines.
IGNITION VOLTAGE OUTPUT TEST
Scopes may be inaccessible from time to time, so we at "Bubba's Garage" have come up with this here test for Ignition Output:
1.Hold medium wrench in one hand, Sears wrench preferred for accuracy of test 'cause other smooth wrenches are too slick for throwin'!
2.With engine runnin', grab hold of the plug end of an ignition cable with the other hand and hold on tight!
3.This will more than likely cause you to throw wrench! KV output is based on how far the wrench wuz thrown!
10 feet = approx. 10,000 volts
20 feet = approx. 15,000 volts
30 feet = approx. 25,000 volts
Over 30 feet = Caution! Must be one of them new
dis-is-it ignition systems,
use bigger wrench and retest.
WARNING! No side effects have been reported due to testing at this time (although it has been known to kill chiggers after berry pickin')
Bubba Sez: Electricity will not usually hurt you, instead it is the back of your neck going through the hood latch that really ruins your day