Have someone else crank the engine while you check the voltage at the + side of the coil wiring. It should not be below 4.3 volts with the starter turning. Then check the battery voltage at the posts (not the terminals) while cranking. If the battery voltage is below 4.5 with the starter turning recharge or replace the battery. The voltage at the coil should be within .1 to .2 volts of battery post voltage. If it's not, find the high resistance connection(s) between the battery and the coil- - - -ammeter, ignition switch, wiring connectors, etc.
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!