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MG MGB Technical - Alternator ?

The Ignition Warning Light on my 73 B satys on even with the car idling OK. So, I'm told the alternator mite be defective. I'm limited on my expertise, so the question is, should I drive it up to a local AutoZone to have it checked or take it off to have it checked or is there something I can do at home? And are there any pitfalls/difficulties in removing the alternator (any special equipment needed?).
John

Certainly the warning light staying on is the usual symptom of a failing alternator. If you can get hold of a multimeter, or know a friend who has one, you can measure the voltage between the alternator terminal and earth at idle speed. This should be at least 13.5 volts but not more than 14.5 volts. If its less or more, the alt is faulty. Taking the alt off is simple. Disconnect the battery earth lead. Pull off the connections at the rear of the alternator. Loosen the three bolts that hold the body of the alt. Let the alt hang loose and remove the drive belt. Then supporting the weight of the alt, remove the three bolts and you have it in your hand.
Mike Howlett

John - If you are going to have someone check your alternator, take it to a real auto electric shop (there should be on in your area), not to some discount store, where the person may or may not mknow anything about an alternator, other than the fact that it is used in a car. Cheers - Dave
David DuBois

John-
What does that ignition warning light that is labeled ‘ALT’ on the dashboard indicate when it comes on? Quite simply, it means that the alternator output voltage is either higher or lower than the battery voltage. If the light becomes dimmer as you increase the engine speed, then you have a problem with the alternator. If it gets brighter, then the battery is most likely bad and the problem can be cured by simply replacing the battery.
Steve S.

Dave. Understand your warning, but in out town, the auto parts store actually is not bad. They have some new computer controlled testing systems that really are just about idiot proof. Nice think I like is if they say something is bad and you buy it from them. If that does not fix the problem, they take the part back.
Bruce-C

I had the same thing on a customers car which tuned out to be the ignition switch relay, can you believe?
Al
Allan Reeling

You say idling, but an alternator won't start to charge until it is revved to about 900 rpm or more, thereafter it should charge at all revs down to about 600 rpm, it which point it will 'drop out', and have to be revved again. If the only time the light stays on is immediately after starting and before you have revved it, but goes out and stays out when revved, that is completely normal and it is working as it should. But if the light stays on while you are driving, then there is something wrong that needs further investigation.
Paul Hunt

This thread was discussed between 01/08/2009 and 02/08/2009

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