The charging system on my 83 300D Turbo seems weak. It has a new altenator, but the battery light still comes on and off, especially at idle. Where should I test for voltage? The rear of the altenator? What should the readings be? Thanks for your help.

Easy to test at battery connections. Look for +14.4V at idle

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How tight is the belt? Check you ground straps as well.

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The belts are tight. Very little deflection. I'll check the voltage and the ground strap tonight. Thanks.

EDIT: Oops, I need the new alternator part.

Might be something else, I assume the new alternator came with a new voltge regulator. Have you checked the ground connections (battery to ground, engine to ground)?

Be sure your idle rpms are where they are suppose to be...

All of this info is a bit in the past, but, some US vehicles suffered from "ghosting" of the alt light from the difference between battery voltage and alternator output voltage. If the alt put out 14V and the battery was 12V, the light would get 2V and you could see it at night.

I presume that the M/B has diodes to prevent this occurrence, and the diode might be fried. If the alt. puts out 13.5V at 1500 rpm or more, I wouldn't worry about it.