low/no charging

Hello!

I'll try to explain my problem the best I can for you guys, and hoping someone can help.

When It comes to diagnosing electrical problems, I spend more time scratching my head than actully doing some work.. I have no idea where to begin..

My 67 Dodge Dart doesn't charge propelly. Or I think that is the problem... I've tryed measuring the battery when the car is running. It measures 10.2V. Directly on the alternator It measures 0.08V. I've also tryed with a testing light between the negative pole and negative wire, the light lights up. Then unwired the alternator, and the light still lights up.. That indicates the alternator is OK, right?

I have a 70ah battery. I tryed to switch it out with another big *** 70ah battery that puts out power like 2 batterys (measures 25V while car is off) problem stays the same, so I dont think it is my battery. The car still doesn't charge more than around 10v with that battery.

I asked a mechanic for some help. He said I should disconnect the negative wire on the battery again and put the testing light between the pole and wire, then pull one fuse at the time, and check when the light doesn't light up anymore to find witch circuit Is bad. (Not really sure I understood him correctly) This I haven't done yet, because I think that would be a real pain to find. The fuse box on my car is aftermarked, and have no idea witch fuse is for what circuit.

Sorry for my bad english, hope you understand.