The next time this happens, the goal is to keep it not cranking. Do not try to get it to crank because then there is no defect to find. Use a digital voltmeter to measure the voltage to the starter. Put one meter probe right on an unpainted surface on the engine block, and the positive probe on the larger terminal on the starter. For convenience, I use a small jumper wire to connect the positive probe to the starter terminal so I do not have to hold onto it.
You should find full battery voltage of 12.6 volts. Now watch what happens to that voltage when a helper tries to crank the engine. During cranking, expect the voltage to drop to as little as 10 volts. That is normal. What we are interested in is what that voltage drops to when the starter fails to crank the engine.
An additional clue is to observe how much the head lights dim when the starter does not work.
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Wednesday, November 8th, 2017 AT 4:47 PM