Measuring voltage is not the way to verify alternator output. Amps output is the measurement. A fully charged battery will not need much voltage hence a low voltage reading. Have it tested for amp output above idle with a load tester like a VAT 40 or something similar at a shop. If, as you increase the load, the amps rise, then its working correctly. Its VERY important that the drive belt is tight. With the engine off, try to rotate the alternator pulley the opposite direction of normal rotation with your hand. If you can move it, the belt is loose! Also make sure the ground cable to the inner fender is clean by removing it there and cleaning the surface.

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81 300CD (sold) 1972 280 SEL 4.5 (sold) 1966 250 S 4 spd (sold) 1974 450 SL (sold) 86 BMW 325ES (sold), 1973 280C (sold) 1988 300 SE.