I have a question that’s bothered me for a long time. I’m sure there’s a simple answer that I’m just missing. A common alternator test (on cars with no ECM) is to pull the negative battery cable while it’s running. Here’s the question..when you remove the negative battery cable, are you not removing all grounds on the engine? If the block is no longer grounded, then the plus aren’t grounded so how is there any spark (no ground to the coil either). Like I said, probably missing something...

Alternator Test Question