No-No-No- - - - -"read my lips"- - - -the distributor side of the coil is the NEGATIVE (-) terminal unless somebody has reversed the polarity for some reason. You're not running a 6 volt GMC, are you? The POSITIVE side of the coil is the wire that comes from the ignition switch, and should have dropping resistor voltage (about 9V while running) for a 55 2nd. series Chevy 6 or V8, or battery voltage for a 55 1st. series 6 cylinder.

The only time the distributor side of the coil would be positive would be a 6 volt GMC or a pre-1957 Ford. Put the red test lead on the wire that goes to the distributor, and don't worry about the polarity- - - -it should measure dwell properly at either polarity.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!