The battery went dead on my 1983 380SL, so I replaced the seven year old battery and checked the charging sysytem, as best I could with tools available (digital voltmeter). I was distressed to see only battery voltage at idle, with no change when I revved the engine to 3000RPM. I checked to see if the battery light in the dash worked in the #2 position, which it did, so I performed the only crude test I could think of, taking off the alt belt to see if the batt light would come on when I started it, which it did. This shows the warning system is working. On GM vehicles, I routinely see 14-14.5 volts at the battery at idle, even on a charged battery. Any ideas?

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1983 380SL
1995 C280
1995 S500 coupe
1990 Mazda Miata
2004 Suzuki Hayabusa

Most cars I've seen will show that higher 14V+ at idle as well, then drop to 13 something when the motor is off. Maybe your multitester is bad? I tossed one last week because it was reading 17V on all my batteries.
A good alternator test would be to turn on all lights and A/C on high to see how she handles the load.

Thanks for the reply, Chevota. I did check my other vehicle with the same meter, and it read 14.4v. I tried turning on all the accesories I could think of, checked voltage at the battery, at C105, which is where the pigtail from the alternator hooks to the batt/starter circuit (on the coolant expansion tank bracket), and at the big batt cable connection in the engine compartment, and I read about 3 tenths lower, about 12.3v. I also checked continuity on the alt pigtail lead, checks good. I'll try to get a meter to measure amps from the alt to see if indeed I have a problem. My wife thinks I'm creating a problem where there isn't any. Some women just don't understand a good old need to fix something

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1983 380SL
1995 C280
1995 S500 coupe
1990 Mazda Miata
2004 Suzuki Hayabusa

Check the voltage regulator on your alternator. If the brushes are worn down, the alternator is not recharging the battery. Cheap part to replace.

It may be on its way out like jriewer said. If it's the original alt then I'd say you got your money's worth. You sound like a do-it-yourself kinda guy, you might consider rebuilding it yourself. I have a local hole in the wall starter/alt repair place that sells me any part I need for cheap.
Also, most auto parts stores will test your alt for free. They'll give you an amp and volt reading.

Thanks, guys. It's a very easy one to remove, so I'll do that and have it checked. Thanks again for the help.

Paul

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1983 380SL
1995 C280
1995 S500 coupe
1990 Mazda Miata
2004 Suzuki Hayabusa