New w123 owner- with battery issues

[dinman]

Hi guys. New here.

I recently acquired a 1983 300D for a very, very good price. But it needed work, and has been somewhat neglected.












Prev owner installed a new positive battery cable, and a new battery on March 10th 2017. I just got the car two weeks ago. SO the battery is basically new.

SO the car has had a very dim battery light since i got it. But always started with no issues whatsoever. bright headlights, no dim interior lights, horn sounds good, etc. A few nights ago, i changed all 4 of the belts. After doing so, it seems the alternator wont charge. Or i should say, won't charge very well.

Now before, the belts were literally flopping around. They are nice and tight (not too tight) now. Immediately, i noticed the car was not wanting to start rapidly like it was. So, i checked the ground cable, and the contact around the post on the battery was literally broken in two. I felt relieved and went and got a new ground cable.

That did not fix it

I'm reading 12v when turning the car off, around 11.7 when it sits for 30+ minutes. and 12.3-12.6 when idling. When i rev it up, 13.1-13.3. Nothing higher.

I pulled the voltage regulator, and both brushes are there, but one is slightly shorter than the other. Was planning on replacing that for the hell of it.

I also have a w212 e63 amg, i remember when i first got it, replacing the voltage regulator remedied all my battery issues.

Also, i am an idiot and hit the alternator plug with a wrench, and it sparked. Hate to even say it, but it may help in diagnosing the issue. Is there a fuse/relay for it i may have blown? any cables to check? etc?

I'm new to this car and the w123 chassis, so any help is greatly appreciated. Trying to get this thing on the road to keep miles off of my E63

[Elektri]

I would replace the alternator.

[Ferdman]

dinman, start by replacing the voltage regulator. Then proceed to replace the alternator, if necessary.

[sixto]

Consider an alternator upgrade. I hear the 100+ amp alternator from certain Saabs and/or Volvos is an easy swap in place of the 65 or less amp sticker.

Sixto
83 300SD
98 E320 wagon

[Dmitry at Pelican Parts]

Hello and welcome to the forum - if you're planning on replacing your alternator, check out the link below to our site's DIY article on this process. If you have any questions, please feel free to post a Comment just below the article and we'll do our best to give you specifics with more details. Best of luck!

Mercedes-Benz W123 Alternator Replacement | 300TD 1977-1985 | Pelican Parts DIY Maintenance Article


-Dmitry

[dinman]

thanks for the answers everyone

[Mxfrank]

With the rotor out, dip a piece of wet or dry into alcohol and clean the slip rings. Sometimes this can be caused by an accumulation of carbon and oil. Then install a new regulator.

If that doesnt do ir pull the alternator and bring it to a parts store for testing and probable replacement.