Alternator not charging

You can prove your alternator CAN work by full-fielding it. You run a jumper from the battery plus to the field terminal, and then ground the second terminal. You will connect the ground, with the engine running, the battery recently charged and a VOLTmeter previously installed across the battery, and all accessories turned off..Alt output must be higher than battery rest voltage by at least 1.25 volts, and increases with rpm. Do not go crazy with rpm, you might blow the ignition module. If it makes the minimum, consider it to be ok.

I connect the ground last while watching the voltmeter, and as soon as I see the voltage, I disconnect the ground. In this way I prevent damage to sensitive components. The charge circuit itself will happily work at 15.5 volts, and mine has withstood 17 volts on occasion. But the headlights didn't.