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  #1  
Old 10-04-2009, 07:01 PM
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Alternator Blues - '71 220D

Alright, it seems my old alternator just wasn't putting out enough juice to recharge my battery on my 220D. I got a new Bosch one in, wired it up like the old one, and I'm still not getting enough juice (barely putting out 12v). I'm going to remove the alt and have it tested individually tomorrow, but this is the least of my worries.

I'm having a hard time finding any sort of picture or diagram to how the alt is supposed to be wired. There's a few things that are making me scratch my head that I could use some help with...

1.) There seems to be two possible places to connect the positive cable (both labeled B+).

2.) There's a small black box bolted onto the back of my old alternator, which as a single black wire leading from it. On the old alternator, this was connected to the B+ connector, which is where I connected it on my new alt. What is this part? (I'll try and get the part number off of it)

3.) The connector on the bottom of the alternator (3 connections, labeled DF, D+, and D-) is different from my old one. The old alternator had flat-pronged connectors. The new one has circular connectors.
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Old 10-04-2009, 11:40 PM
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Barly putting out 12v; that is just the Battery Voltage.

I do not know the set up on the 71 but on my 84 300D if the Charging Light Bulb is no good or there is an open circuit in that charging circuit my Alternator is not going to charge.
It need to have the Light Bulb working to excite the charging circuit in the Alternator.

You might find out what vehicle the newer Alternator was supposed to go on and look up the Wiring Diagram for that Vehicle.
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Old 10-05-2009, 12:38 AM
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If you can send a pic of the back of your Alternator where the terminals are.
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Old 10-05-2009, 08:22 AM
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Your old car has external regulator but you are installing a newer alternator that has built in regulator. You need to do some re-wiring to make it work.
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  #5  
Old 10-18-2009, 04:31 PM
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73' 220d similar problem

I too want to know what that flat rectangular module with a single wire is on the back of my alternator. I think we both know we have an external regulator attached to the firewall area. I just burned out two alternators in two weeks. I had a new rebuilt bosch alternator installed by a professional after installing a fast glow plug set up. I'd go back to him, but after many years, he just closed up shop and moved away. I replace that one myself with another bosch rebuilt, and I'm very sure I reattached all wires the same way. But, of course, maybe I didn't, so I'm in the same boat as the original poster. After the new alternator is fired up, it only takes a couple of restarts before the alternator dash light goes out, and I assume the alternator is again burned out. I had the previous one bench checked to find out for certain. Also, is the alternator supposed to be mounted with a bushing? Mine is not.
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Old 10-18-2009, 11:41 PM
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Single wire small module on the back of the alternator is probably a noise supression capacitor. If it has a visable part number on it you may find it in the manufactures parts list. If you have a meter that reads capacitance you could see if it reads. Another way of identification is on a very high range ohm reading you might see the chargeup till your meter reads open or infinity. The black lead has to be disconected for that test.

The capacitance checking function is starting to show up on many cheaper meters reciently. Not a particular lot of use for the average guy but nice for checking ac motor capacitors and a few other things out from time to time. For example a lot of portable generators have capacitors and they can be failure prone.
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Old 10-19-2009, 02:27 PM
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Thanks...I thought it might have something to do with noise reduction (static).

Now if I could just have an answer to whether or not my alternator attaches with a necessary bushing. By the way...Rusty at BuyMBP informs me that the replacement alternators now come with a smaller sized housing hole for mounting. If that's so, isn't the alternator subject to some "play" when attached to the engine mounting?

Also, why might my alternator be burning up quickly? Should I be leaning toward a power surge taking it out due to an open or expose wire some where, or some other cause?

Any ideas to suggest would be appreciated. I'm a novice at this and will probably take it to someone who specializes in auto electric, but I'd like to have some idea myself so I don't sound totally ignorant when discussing this. Do you think I should take it to a MB dealer service department?
Thanks for any podering and replies
Ken
'73 220D
New European head
New fast glow setup
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Old 10-19-2009, 02:33 PM
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Auto electric place should be at least as knowledgeable as the dealer and somewhat less expensive unless you hit a den of theives. Your problem is a walk in the park for an auto electric type usually. Although it's up to you to find an ethical shop.
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Old 10-19-2009, 05:11 PM
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Quote:
Originally Posted by dackwood@tds.ne View Post
I'd go back to him, but after many years, he just closed up shop and moved away.
There are laws that give you recourse in this case. Depends on where you are, but there should be legal means to compel your mechanic to get it right once you've paid for his service.
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