Stepsons car would not start this morning. However, it started with a jump. I suspect he left the dome light on, but he says no. He claims it was dead as a doornail, no dash lights etc. Anyway, I have noticed that the battery light stays on after start up, until you get it just above idle, then you get normal charging voltage. Oh, it is a 1990 244 N/A manual transmission.

Before you get the idle up, and the battery light goes out, battery voltage is only 11.50 while running (approx). Once you rev it a bit and get the rpm's up just above idle, it charges at 14.10. Voltage regulator/brushes in alternator possibility?

Also, I notice the speedo needle bounce up when you first turn the ign. key.

Swapped battery out with a known good one. Even though the car charges at 14.10 (once you get revs up a little) the original battery was struggling to start the car as I was my running various test, starting the car several times.

Note: when I say get the revs up, let me clarify: Turn key to first position, all dash lights light up, start car up battery light stays on, 11.90V at terminals, touch gas a little battery light goes out, 14.10v at battery terminals with car running, and you can hear the alternator make it's whirring noise like it is charging, because it is. Once the revs are up enough to make battery light go out, it stays out.

Also, as mentioned the speedo needle jumps when cranking

How many volts should I have at battery terminals when cranking? I think the starter may be drawing too many amps possibly?