Re: Charging System
Does the idiot light work? Key on, engine off, it should come on. A burned out bulb can do your complaint. The bulb provides initial field current.
Test to see if it can charge on the velhicle by bypassing the internal regulator. At 12.5 it isn't charging at all - the light should be on.
Look on the back of the alternator - you'll see lots of vent holes but only one in the shape of a "D" about 3/8 diameter.
While running at idle watch the votage while you push an allen wrench or small screwdriver in through the "D" hole (no, you won't hit any rotating parts if you are in the right hole.) It'll go in about 3/8" then touch something - the connector tab for the regulator. Touch the tab and lean the wrench so it touches the tab and ground at the same time. That bypasses the regulator and should make it charge. Voltage should go above 13, maybe as high as 15 at idle. That proves the output is reaching the battery OK.
Then check the side connector.
Engine off, key on, unplug the side connector. Measure the voltage with key on. Both wires should have 12 volts on them.
The red is the "sense" line for the regulator - to decide whether to charge or not - should go to the "hot" terminal block on the firewall or to the starter "big" terminal.
The white or brown wire, goes to the idiot light. Key off it should read 0, key on 12 volts. That wire goes to the light, the other side of the light goes to switched ignition.
And - look close at the big wire from the alternator - sometimes there's an in-line fusable link about 6" from the stud connector. Disconnected that wire should also read full 12 battery volts.
It's a simple system, hope this helps.
Let us know what you find.