My battery went dead on me a couple of times lately. My alternator light comes on at idle and doesn't go away until I rev it up quite a bit. I checked the voltage on the battery and it goes up to about 13.5 volts while I'm reving the engine so it looks like I've got a charging problem only at idle.

Here's my question: Do I have to replace the alternator or may it just be the voltage regulator? How can I check which one it is?

Thanks,

Scott

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Scott
1982 Mercedes 240D, 4 speed, 275,000
1988 Porsche 944 Turbo S (70,000)
1987 Porsche 911 Coupe 109,000 (sold)
1998 Mercedes E300 TurboDiesel 147,000 (sold)
1985 Mercedes 300D 227,000 (totaled by inattentive driver with no insurance!)
1997 Mercedes E300 Diesel 236,000 (sold)
1995 Ducati 900SS (sold)
1987 VW Jetta GLI 157,000 (sold)
1986 Camaro 125,000 (sold - P.O.S.)
1977 Corvette L82 125,000 (sold)
1965 Pontiac GTO 15,000 restored (sold)