alternator help, please

[LFrank]

The one-year-old battery will not charge while driving (but will hold a charge from a trickle charger); the red "electrical current" light on the indicator panel now lights up while driving; and the car cannot be restarted without a jump.  

To my untrained eyes, this looks like an alternator issue. Easy/hard to find/replace? Hideously expensive to boot??

Thanks in advance for comments from the crew!


LFrank
Washington DC
65 230 sl - auto
DB334/Hellblau

[J. Huber]

Hey LF.

I can't say for sure that your problem is the alternator but I had a battery charge issue myself a couple of years ago. My mechanic found that my alternator was outputting very low amps ... he sent it off to be rebuilt. Total (inc labor @$70 hr) came to 290. No problems since.

James
63 230SL

[ja17]

Hello LF,
The alternator or regulator should be the issue normally. Frist make sure the battery cables are clean and tight and the other connections at the alternator, regulator and engine ground are good also. You can get a spray electrical or battery cleaner at your local NAPA to clean up the connections and plugs.
My first guess would be the alternator brushes. These Bosch alternators are no big deal for any automotive electrical rebuilder (usually several in any city).  Also you can also go to your local Bosch dealer (import auto parts store) and order in a Bosch Factory Rebuild for a little more (but still reasonable). If you go to the MB Dealer they will be high, in this case they are the middleman between you and Bosch.
These  W113 cars have a separate regulator on the right side of the engine bay (metal can 1 1/2" X 2". These can also be at fault or may go bad along with the alternator. The alternator comes off easily you may want to remove it and have it checked out.
If you need any documentation on this alternator (Bosch blow ups, parts lists with Bosch numbers, rebuild or testing procedures) let me know I have Original Bosch and Mercedes documentation on the unit. Good luck!


Joe Alexander
Blacklick, Ohio

[Malc]

Agree with everything stated here, the charging system is very similiar to the system used by BMW from around the same time, surprise surprise.
Make sure that the case of the alternator is earthed (grounded) to the engine, usually by a small wire. THis sometimes breaks, falls off contacts corrode.
This happend on my 2002Tii and same problem it would not charge the battery, the alternator on that car has rubber bushes to "isolate" it and reduce vibrations hence the earth or ground strap.
I could be talking complete nonsense but somebody will probably put me right!
Cheers
Malc

[Naj ✝︎]

Well Malc,
Guess what!!
The 230 alternator also has rubber bushings in the main mounting bracket. So 'ground' could be an issue
naj

'Kloines Scheisserle'
65 230SL
68 280SL

[n/a]

Since you are in the area, I recommend Mamock's Motor Electric, in Annapolis. They do this all the time, they do both auto and marine alternators and starters, as well as A/C, and I have found them to be knowledgeable and honest on pricing. They rebuilt the alternator in my Ferrari at a fraction of what it would have cost to get one from the dealer or manufacturer. (turns out it is an AC Delco unit also used on GM pickup trucks).

[Malc]

Naj, and everybody else!
The cars have a remote voltage regulator, Am I correct??? If they do then I am pretty sure that it should have a seperate earth, you can use abit of wire as a temporary earth strap start car and see if it starts charging
BTW you can get brushes etc for older Bosch units for pennies, Many people make the mistake of exchanging an alternator which costs a fortune when 10 minutes of "home" investigation will show little wrong. My daily hack has had three sets of brushes on the alternator, 233,000 miles. Bearings et al are fine so a good clean up and in with new Brushes, £3.75 a set, exchange alternator £110

Finally make sure that the earth strap from the engine to the body is in good shape too. If you have a multimeter place on battery negative and then on a clean part of the alternator case should be zero Ohms resistance, or maybe one or two. If higher investigate! Simple tests which could save a fortune!
Hope this helps
Malc
Sorry went on abit again!

[Cees Klumper]

SLS in Germany lists a 'repair kit' for the alternator at 5.20 euros. A new alternator (55A) lists at 365 euros.

Cees Klumper in Amsterdam
'69 white 280 SL automatic

[Ray Ortiz]

I upgraded my alternator to a 55 amp from a newer MB., changed the plug and disconected the old regulator.  Now the top red light in the dash stays on when car is off and ignition is in the off position.  When ignition is turned on the light goes off but the alternator is not charging the battery.  Alternator tested working properly.  Any ideas....?
Could it that maybe is not grounded like suggested previously...?
I' ll try that.............help!

[ja17]

Hello dirianghen,
It sounds like you are not wired up correctly. The field wire going to the alternator runs through the red dash light. The field wire must be energized when the ignition is on in order for the alternator to charge. The fact that your dash light is on when the ignition is off means the field wire is energized when the ignition is off instead of when the ignition is on like it should be.  Check your wiring. Get a test light and disconnect the plug at the alternator and see if you have a field wire which comes on and off when the ignition switch is turned.
Make sure the alternator is grounded as mentioned in earlier posts.

Joe Alexander
Blacklick, Ohio

[tuultyme]

I bought a rebuilt 55 amp alternator from Ray Paul at SLClassics this past summer for my 1970 SL.  The bearing went out on the old 35 amp.  I did not have to change any plugs, just installed it and plugged it in.  I did replace the voltage regulator with a new one just to be sure everything was working fine.  The alternator light glows faintly at a stop light in gear because the engine is idling a little low; car's tach is off on the low end.

Bruce; Blaugrun(green) 1970 280SL; IL

[n/a]

A little late maybe, but it might still help.
 
I had battery charging problems a while ago. It turned out to be the alternator, who had a faulty field diode, the red warning light never went off completely, the battery died slowly. Also the mechanical Bosch regulator had burned in contacts. I had the alternator overhauled by a retired car electrician, and replaced the regulator with an electronic one : CAR GO nr. 130675. It's 1/3 of the height of the Bosch, the installation holes match, and I paid 35 Euro's.
I also have a 77 Ah battery since 5 years now, problem free till now, (1500 km's a year).


Willy, 230 SL 1967 - 220 SEb 1965

[Bob G ✝︎]

I replaced a 55 amp alternator form a 107 chassie back to the 35 amp alternator with a new voltage regulator. a friend of mine said he could wire a new pingtail for the newer alternators that have the self contained brushes and regualtor, however at this time I did not feel the modificiation was needed and this was a simple inexpensive fix to get me by since I only drive my car on rare occasions.One more thing is I would not recommend the Mercedes-Benz batterys they cost too d"""m much and do not last purchase an interstate battery they have a very popular battery that fits and will accept the metal battery top hold down plate.

Bob Geco