77 240D alternator/ charging questions
 

Hey guys, I'm new to MB so I'm not exactly sure what the charging sytem should put out. Just bought the car. Drove it two days. Started fine this morning and @ a few other stops, then I had to jump it to get it to start @the grocery store. Looked at it tonight. Battery had just over 12v but would not even turn over engine. jumped it and took a reading at the battery and there was no change. Shouldn't the volts go up when I rev the motor. I turned on the lights and volts dropped to 11.3. I'm guessing that the battery is not getting a charge and lights and etc is running off the battery. I've read a few threads and not sure if I should be looking at the alternator, or the V/regulator. Battery is new and the cable from battery to starter is new. I know the juice is getting to the starter, readings were the same there as on the battery. Also I read on here somewhere that a guy was having similar problems and went through all the regular stuff and it ended up being his battery light on the dash. sounds goofy, but I don't know these cars that well yet. By the way, I've already learned alot from you guys, so thanks alot. Curt

Definitely sounds like it's not charging. Yes, the volts should go up at the battery as you rev the engine. Yes, the dash light is integral with the charging system. If it's not lighting up when you first turn the key, the system is not charging.

cycleboy, thanks for the reply. Does the dash light actually do anything beyond let me know the system is working? What kind of reading should I have when the engine is idling. If the system is not charging, where would you start at, v/reg, alternator, dash light? thanks again for your help. Curt

Yup..
 

The dash light DOES play an integral part - as it was described to me, it completes the circuit, so as to tell the alternator to engage. That was my problem....could also be a regulator, or even the alternator itself, but start with looking at the bulb. If it doesn't turn on when you turn the ignition switch, I'd guess that to be your problem. That would be a cheap fix.

OH..
 

and mine, with a new alternator, reads somewhere in the vicinity of 13.5-14v at the battery.

Thanks barrylnd, I took the alternator off and had it tested today. Test showed it only produced 11v or so. The dash light works, but only when the battery is fully charged. Hopefully the new altrnator and v reg will solve this whole deal. I guess I really need to get a good manual. Any suggestions a good, thorough manual. Thanks Curt

Curt,

Buy the factory service manual on DVD from the MB Classic Center. It's more comprehensive and is usually cheaper than Haynes or Chilton.

(geez, and for as much as I say this, I think MB oughta start givin me a cut).