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Sun Apr 26, 2020 1:55 pm

As I do more research for my electrical harness I was looking at my alternator the part # is 120 400 836, when I look it up online is says its an internally regulated alternator, but when I was pulling out the rear seat I found what looks like a regulator and the wires are routed to the engine compartment and are connecting to the alternator, I've included a picture of the alternator and the regulator under the seat. So do I have an internal or external regulated alternator?

Sun Apr 26, 2020 2:21 pm

Whenever you have a three wire plug on top of the alternator, it is externally regulated. And yes, VW number 043 903 023A part number is a Bosch externally regulated unit.

Sun Apr 26, 2020 2:24 pm

Yes it is external. Surprising to see a Bosch, I thought all the external-regulated ones were Motorola. I guess not all. :D

Sun Apr 26, 2020 2:31 pm

I've previously quoted one of the VW "Bibles" - the J.T. Garwood, Car of the Century book, in previous thread. It seemed to indicate that Bosch Alternators went with Bosch regulators and likewise with Motorola.

glutamodo wrote: Different manufacturers of the externally regulated alternators is the answer. It's laid out in the "Car of the Century" Garwood book, I've referenced it before when I've said:

043903023 was a Motorola alternator and went with a 043903803 Motorola regulator.

043903023A was a Bosch alternator and went with a 043903803A Bosch regulator.

I seldom take scans from the COTC book but I have one for this:

Sun Apr 26, 2020 2:33 pm

I haven't seen one of those in a beetle usually the external VR Alternators here in the US are Motorola. I think it can use a generic VR the Motorola does. Probably find one at the local auto parts store. https://www.rockauto.com/en/catalog/volkswagen,197...lator,4884 As for the cable I would think it's going to have to be a used one someone could have or just use spade lugs you could move it to inside the engine compartment.
From the looks of things the a lug inside the connector caught fire and for that to happen I would think the Alternator burned out too. New Alternators will have internal regulators and you won't need that cable. Well unless you find a rebuilt one like your alternator.

Sun Apr 26, 2020 4:07 pm

Be careful as you look up part#s. AL-78 (or AL78X) is a common generic reference for the external regulated alternator. AL-82 (or AL82X) is commonly used for internally regulated alternators. But then you see references where they are used interchangeably. This could be because the AL-82 superseded the earlier AL-78 as a replacement part. It saved on the need to stock the extra external VR as part. You can install an AL-82 alternator in place of an AL-78 with just some simple re-wiring (splice two wires together). But an AL-78 cannot replace an AL-82 without also adding the external VR and all its wiring. Because the AL-82 was used in more model years they tend to be easier to find and often cost less. The FLAPS near me can order both but the AL-78 takes longer to get.

Sun Apr 26, 2020 4:29 pm

Currently the alternator is working fine with the regulator that is installed from what I can tell; I recently removed the battery and placed it on a charger for a few days, because the car is sitting on blocks while I work on other things. I reinstalled it yesterday to start working on the engine, checking the timing and other overall checks which included checking the voltage of the battery with the engine running and I was reading about 14.3 volts, so the alternator is giving a charge to the battery.

So with my searching around the car of what is installed and what I want to add to the car, I have determined that I will be going with a modern fuse box that will give me the space for expansion to include seat heaters and a 5-8 Kw diesel heater.

I assume that the regulator must be kept from the weather instead of being placed in the engine bay closer to the alternator?

Thank you all for the input about the regulator.

Sun Apr 26, 2020 4:47 pm

sjbartnik wrote: Yes it is external. Surprising to see a Bosch, I thought all the external-regulated ones were Motorola. I guess not all. :D
My current one is a Bosch and so is my spare.

Sun Apr 26, 2020 8:06 pm

yes BOSCH and MOTOROLA had different wiring for the external VR. You could get an adopter to fit one or the other. I have one in my stash I think.
https://www.thesamba.com/vw/forum/album_page.php?pic_id=732312

Mon Apr 27, 2020 7:44 am

the original motorola regulator you have pictured was a sealed electronic unit and shouldnt be adversely affected by mounting in the engine compartment but of course the plug isnt sealed and could be subject to corrosion....ghias and buses had their regulators in the engine compartment...6v cars sat them on top of the generator and i've seen plenty of 12 v conversions with the regulator screwed to the fan housing....i think the back seat location was done more for space limitations in the engine compartment than for weatherproofing

Mon Apr 27, 2020 7:54 am

My Bosch alternator has a Motorola regulator. It's been that way since 1974 when I bought it new.

Mon Apr 27, 2020 9:11 am

60ragtop wrote: yes BOSCH and MOTOROLA had different wiring for the external VR. You could get an adopter to fit one or the other. I have one in my stash I think.
https://www.thesamba.com/vw/forum/album_page.php?pic_id=732312

I've been wondering forever why there is this short wire adapter between the Bosch regulator and wiring harness. So now I know it is there to be able to switch the production between Bosch and Motorola without needing a different main harness.

According to the linked document it is possible to mix Bosch/Motorola on alternator and regulator. Good to know.
I thought I had seen a VW document that said both parts should always be from the same manufacturer.

Does anyone know if it is possible to convert a Motorola alternator from internal to external regulator?
I have one in my stash from a '79 SB and would like to use it in my (very early) '75 SB which still has the external regulator.
On pictures the Motorola alternator internally/externally regulated looks pretty much identical aside from the regulator/brush holder.

Mon Apr 27, 2020 10:09 am

Maybe this will help somebody in the future. This is the current external VR used for my 74 bug with a Bosch Alternator

Mon Apr 27, 2020 3:52 pm

Here's an old post about someone trying to get a US-spec Ford VR to work in place of the VW VR.... it apparently worked:
https://www.thesamba.com/vw/forum/viewtopic.php?t=573162
Conceptually the VR works the same so in a pinch you may be able to use a VR-166 part# from any US FLAPS as the VR for your Bosch or Motorola AL-78 alternator. I've not tested this myself so YMMV.

Tue Apr 28, 2020 10:48 am

The Motorola Alternators came in a couple of configurations one was with the regulator mounted to the outside of the Alternator. I think parts may be interchangeable between the two configurations.
VW and Dodge Jeep and Ford in the mid 70's used "B circuit" regulators. Where "A circuit" regulators regulated the Positive power feed to the Armature and "B circuit" regulators regulated power between the Armature and ground.

Motorola Alternators have the Diodes inside:

Motorola Alternator with Regulator attached:

Motorola Alternator that uses a separate mounted external regulator:

Wed Apr 29, 2020 5:56 am

Danwvw wrote:
Motorola Alternator with Regulator attached:

Motorola Alternator that uses a separate mounted external regulator:

Pictures like these made me think that it could be possible to replace the regulator with a 3-prong brush holder to convert to an externally regulated Motorola alternator. Has anyone tried this?

Thu Apr 30, 2020 11:16 am

I would think the attached regulator would be the way to go: Here is a Classified Search for Motorola Regulator. I have several 3 prong Motorola Alternators and some parts. Usually what goes wrong with the Motorola Alternators is one brush wears down and sometimes they melt an internal diode. The 3 prong connectors tend to get broken due to the fragile nature of the white ceramic they are made from.

Here, one of the diodes melted its solder and fell out.

Thu May 14, 2020 10:24 am

Hey Danwvw, thanks for the pictures and information.
I would like to keep the wiring unmodified. So I think I would need a brush holder and this cover with the 3-prong connector.

I looked at all US ACVW shops that I know. But I seems that these parts are nla. The Motorola alternators were never used in European cars, so no need to look over here for spare parts.

Perhaps I have to keep this alternator as it is and sell it and get another Bosch 3-prong alternator.