Just replaced the alternator on a 75 300D.. Appears there's another problem.

Battery light stays on (brightens/dims based on RPM but is on).. Tested the voltage at the battery terminal and there's only 9 volts coming off the alternator (battery is sitting at 11.5~11.8 volts)... Previous owner indicated the alternator was shot (it looked like the original so I wasn't surprised) but there seems to be another issue..

Suggestions? I'm going to stop by the parts shop and have them hook up there tester at the alternator to see what's coming directly out.. but maybe someone here has other ideas..

Alex

I had a dimming problem related to RPM a while back. I changed the voltage regulator, and it fixed to problem. I would try that.

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In a '79 300 SD & '83 380 SEL: Unless you have bearing trouble, the voltage regulator (5 minute fix once the learning curve is over) is the problem. I believe I paid $29 at a common parts store (the regulator on my car is on something like 27 millon cars). Online, this site, $24.
Make sure you write down the 3's on the old part. I carry a spare. Watch when you remove the old one & remember the porper rotation to install ... you'll see, it's a marvel of German design & I wish all cars had this.
Once you've done this, it is soooo easy.

Is the regulator atttached (part of) the alternator?
..I've ordered the FSM for the car (it's shipped but hasn't arrived)..

Alex

Battery Cables
Grounding Strap esp. Chassis-engine (near the starter)
Terminal connections on fender well.

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Sam

84 300SD 350K+ miles ( Blue Belle )

Without good grounds the alternator looses the ability to transfer the charge. A quick test is to run a booster cable from the negative terminal of the battery to the alternator case or somewhere on the block. Make sure to get a good connection. Just takes a few seconds and answers the Question.

I'm replacing the neg terminal.. It's got the longest pos terminal cable I've ever seen...

I'm also replacing a number of the fuses that look really old..
Is there a charging fuse somewhere on this car?

Alex