[Yosemite Sam]

Stop all the nonsence... Isolate the problem before you waste any more time or money.

Hook jumper cables or a boost box directly to the S/G to see if that is the problem or not (positive to the "A" terminal, negative to a bolt holding the S/G on, negative is the last connection). If the S/G spins the engine over well, your your problem is in the wiring, switch, or (most probably) with your grounds.

If the S/G is good and a new direct ground wire doesn't help, then using your test light or meter start from the battery and check each connection until you get to where the voltage loss is. It really is that simple.

BTW, your battery should be showing 12.5 volts or more.

I don't think I would ever buy one of the new S/G's that are advertised on ebay, take your old S/G's to a repair shop and have them rebuilt, if your old one is beyond repair, buy a used on from someone and, worst case, have it rebuilt. I'm betting that you will never find the quality in a new unit that you have with an older one.