35 amp alternator wiring

[wwheeler]

I have a question about the ground on a 35 amp alternator. How is it wired? In the tech manual, an alternator is shown with a square capacitor(?) on one terminal and is attached just below the voltage regulator connector. There is a screw hole there. Is this the only ground connection?

In the tech manual picture, this ground connection is to the B+ terminal and the hot wires are going to what I would assume is the B- terminal. I am I interpreting this correctly? Seems backwards to me.

Thanks for the help!

[ja17]

Hello Wallace,

If I recall correctly, the early alternators had no plug and all lugs for ring terminals. They had a separate lug for a small ring connector and brown wire from the main harness.  Later alternators had the brown ground wire included in the three prong plug (center bottom position). The capacitor is a radio static filter and yes it does have its own screw ground.

Wiring on the alternator (looking at it from the back, with the back of the plug off) is red wire on left (D+), black wire on the right  (DF) and the brown on the lower center (D-).

Early alternators Bosch #0 120 400 608 (July 63 to July 65) had all lug connections with ring terminals on the wiring harnesses. It was replaced by Bosch # 0 120 400 505 ( July 65 to July 66) and finally Bosch #0 120 400 535  MB part # 002 154 49 02

[wwheeler]

Thanks for the info Joe!

I have a 55 amp alternator on there now and the wiring has been butchered to make it work. My goal is to put the 35 amp back in with the original MB wiring scheme. My car is later ('68) and has a 3 plug with a red, brown and black wire as you stated and these go to the voltage regulator. I have two larger braided red wires, one from the starter and one going to the ignition switch presumably. I am thinking these go the the B+ post.

So what goes to the B - post? Is it just the capacitor that is grounded to the case?

What had me confused is the alternator picture in the tech manual had the capacitor grounded to the case on the B+ post. The red braided wires go to the other post in that picture.

Thanks for the help and Happy New Year!

[wwheeler]

I just received a rebuilt alternator from Bosch. It had a new grounded capacitor (2.2 uF) already attached to the B+  terminal as with the picture in the tech manual. The other terminal has B+ stamped twice (see attached picture) where the "hot wires attach. So the picture in the tech manual is correct. So what is the meaning of B+ on the grounded terminal and B+ B+ on the hot terminal. Seems very confusing to me . I guess having an extra B+ makes it more postive than just one B+.

One other last question before we put this thread to bed. What is the purpose of the wire clip just above the 3 post terminal connection?

Thanks and can't wait to get this installed.

[jacovdw]

Wallace,

That wire clip looks like it is responsible for securing the socket connecting to the 3 post terminal, in other words preventing it from loosening during normal operation.

[al_lieffring]

The Pagodas did not have a B- wire going from the alternator frame to the engine block. There were some Mercedes models (diesel and 4 cylinder motors) that had the alternator mount bracket attached to the block with rubber dampers, so they needed a grounding strap. The ground strap (B-) would have attached to the alternator frame bolt with the double nut visible in the photo above. The second B+ post is redundant, they are both parallell circuits to the bridge rectifyer. so either terminal will do the same thing. The square filter, earlier ones were a small metal cylinder, is there to prevent half wave voltage pulses created in the alternator from making a whistling sound through the radio speaker(s).

[wwheeler]

Thanks for that great explanation Al! That also explains why the extra nut and washer were on that stud. I assumed wrongly that if there was a "+", there would also be a "-".

[wwheeler]

Can anyone tell me the part number for the rubber boots used in the picture? This picture is from the tech section.I thought they were the ones used on the fuel pump, but the neck is too small for the two large wires.

Thanks!

[jacovdw]

Wallace,

Scratching a bit through the EPC reveals the following part number: A000 546 33 35 (description: boot - cable to alternator).

The rubber boots used on the fuel pump has been superseded to an A123 xxx xx xx part number.

Hope this helps