MG Car Repair: Red Charge light, alternator belt, volt meter

Question
Hi Howard,
    When running the Midget and driving around all is charging well until the engine warms up to normal or slightly above ,then the Red indicator light is on bright. The other day it did it and then went out ..tonight it did it again and when I brought the Revs up in a lower gear it dimmed but didn't go out? Until Midget warms up its charging.  What do you think I should check first?  Best to you.
                                            Bill

Answer
Hi Bill,
When the light is on put a volt meter across the battery posts and read the voltage with the idle set high (1500 RPM) If it is not 13.8 to 14.5 v check the alternator belt and then check all cable connections, battery positive and negative including the ground strap between the engine and the body. Then check the wires to the alternator (large brown hot wire and the light trigger wire) If everything checks out ok get a new or rebuilt alternator.

The light is powered by the ignition switch and when the engine is not turning the alternator regulator in the alternator is a ground for the light so it burns. When you start the engine the regulator becomes hot (+) and since the light is then (+) on both sides, it goes out. The light can only burn when the alternator is either not turning (engine not running or belt slipping) or the alternator and /or the regulator is bad.
Howard