MG Car Repair: 1979 MGB Ignition Light, regulator problem, volt meter

Question
About a week ago after a 30 minute drive when I turned off my 1979 MGB the Ignition Light on the dashboard stayed "ON" even after I removed the key.  I put the key back into the switch and started the engine, then turned off.  I ended up disconnecting the negative terminal on the battery.  I also noticed that when I turn the key to the on position before engaging the starter the Ignition Light does not light up.  Is this a problem with the Ignition Switch or Alternator circuit?

Answer
Hi David,
The Ign. light is not anything to do with the ignition system, it is a charge light. To test the circuit just turn the key on and note that the light is on and then unplug the wires from the alternator. If the light goes out, the circuit is ok and it is a alternator / regulator problem. To test them plug the alt wires back on and put a volt meter across the two posts of the battery and read battery voltage and then start the engine and set it at about 1500 RPM and read the volt meter again. If it is not 13.8 to 14.5 volts, the alternator or regulator has failed.
Howard