I am in the process of doing some work on my 6.

Old engine has the older alternator that uses the voltage reg on the relay board.


Rebuilt engine has a more modern alternator, with a built in regulator.

There is apparently some way to make it work, but I cant find the bulletin.

More importantly, has anyone "upgraded" to the internal regulator, and what do I need to know / do to my wiring at the alt and at the board.


Also, if you say, just use the old one, I can do it they both work, but it means I have to swap em...

Photo is my current, older alternator. Click to view attachment

Thank you as usual.

On an internally regulated alternator, there will be a blue wire coming from it into the harness. Remove the external regulator from the relay board and hook the blue wire to the D+ connection on the alternator connection plug on the relay board.


Yes, it's that simple.

The blue wire comes from the generator light, and is needed to "turn on" the alternator. The other two connections on the relay board hook the regulator to the externally regulated alternator and are not needed.

Thank you Clay. Somewhere I read there was a resistor that needed to be added to the dash light, is that a requirement? If not, this greatly simplifies my wiring.

Nope. No resistor required.

I did this on the 2.4L engine. It came with an externally regulated alternator, but I changed it to an internally regulated one.

The only resistor is the light bulb. Don't put an LED bulb in there. The alternator won't work if you do.

Clay

Like Clay said it's pretty easy to do.
If you do not have a need for the relay board then remove it.
Get a 911 male 14 pin harness connector and wire it to work with your chassis.
I did this with my brothers 3.0 6 install and worked out great. I also installed a hot start relay next to the 14 pin connection.

Bulletin for the alt is attached. You'll need to modify the rear air flow cover on backside of the alt as well. Make sure your alt gets grounded from a mount stud to the engine block.

On my six, went to a 75 amp alt. It is longer, If I remember I had to have 9mm shaved from the inside of the fan housing (early housing). Again this is with the relay board delete. All works great, plenty of amps, no belt issues now entering the third summer. Mark

If you are using a stock 6 engine harness and don't want to modify it this is
how I did it
My engine is not installed at the moment but the pics pretty much tell the story.
Don't forget a ground from alternator to engine block
Leave the black and white connectors intact but don't attach them to anything.
You can even leave the voltage regulator on the relay board but you'll have to sneak the blue wire into that one female connection.

No luck posting all pics on one post

Please check my work.

I have not buttoned it up, so it is all still "in progress." This alternator has a larger stud, with larger nut Where I believe the Battery / Starter wire goes.

Nothing is labeled other than a "+" and a "-" side of this thing. It seems opposite many diagrams I see.


The ground is just temp till I make sure this is straightened out, but will go from the alt to the case.

The blue wire is where I believe it should go, on the "+" side.


Someone please let me know if I am right, I don't want pretty colors when I hook it up.

Thank you.Click to view attachment

Let me say 1st that I am not intimately familiar with 911 alternator nomenclature

Currently trying to dig up a schematic - info I’m finding in pelican and other places seems contradictory.

My understanding is the blue wire (61) is the field sense / bootstrap wire

According to bulletin - IF I’m reading it correctly shows 61 over on the negative set of diodes along with the negative connection

It APPEARS to me you have the blue wire (61) connected to the positive set of diodes

DOUBLE check me!
Click to view attachment

As mine is connected, yes. Im confused cause the schematic shows opposite in the alternator's layout than what I have. The + and minus are on different sides. Maybe just confirm, that the blue wire needs to be on the negative side then... cause yes, I do have it at the "top" on the positive side...

The blue wire needs to go on the top terminal of the negative (-) side. 2 wires go to the neg side from the harness a Blue and a brown. I do not see a brown wire coming from your harness. A thick brown wire or ground strap also needs to go from the backside of the housing mount stud to the engine block. Only 1 red wire goes on the Positive (+) side. That red wire IIRC goes to the positive side of the starter stud.

I’m not finding a clear schematic

First of all - disregard advice from me above

From some photos I see it looks like those two upper terminals are electrically the same. (This can be checked with a multimeter - see #2 below)

I’m almost wondering if your diodes plates are mis-installed / backward by whoever did the alternator rebuild? Is it even possible for them to be installed improperly? Ugh!

Unless you get clear info from someone that is absolutely sure and has seen these diode plates reversed I think I would contact who ever did the rebuild for clarity.

Alternately I would ohm it out and bench test it with a drill motor to verify which I’m not going to try to outline that setup here.

Maybe some one like @spoke can chime in, he has a 911 and is probably way more familiar than I am

Here’s two things you can do with a multimeter:

1) verify ground - it should be zero ohms between that terminal and the alternator housing

2) you can measure resistance between the two terminals - the one where you currently have the blue wire and the other right next to it. Remove the blue wire to make this measurement if you have the blue wire connected to the car. If the two terminals measure zero ohms between them, it makes no difference which of the two terminals the blue wire is on if they are electrically the same (ie zero ohms between them).

I apologize I can’t be of more use. Who knew there was so much confusion on 911 alternator wiring and so many possible wiring configurations over the years. The fact that your diode plates are opposite of the everything I see is only adding more confusion for me.

Thank you Luke and everyone..

@Spoke maybe you have something to verify here. My understanding is I don't need the brown anymore since I will eliminate the voltage regulator and just run the blue wire to the right terminal.

So it looks like the power wire is correct then, just possibly switching the blue wire to the negative side.

@Robarabian
@Superhawk996

Here's the schematic from my '86 930 with alternator w/internal VR. There are only 3 wires as mentioned before.

B+ goes to the battery. It should come off the + set of diodes.
D- is ground. It looks like the black wire in your picture above has some sort of ground strap to the case.
D+/61 in the schematic goes to the charge light in the dash which is also on the one pin on the relay board where the external VR existed.

Click to view attachment

Here's the GEN bulb in the dash which connects to D+ in the schematic. With the correct wattage light bulb, the resistor across the bulb which was on some models isn't needed. However notice the diode driving from right to left in the picture. The right side of the diode is driven by battery power in the vehicle. This diode was necessary as when the engine was shut off, the D+/61 pin on the alternator would back drive the battery power through the bulb and the engine would not turn off.

On my 930, this diode died and was open circuit and the car was not charging. I replaced the diode with a small diode I had sitting around but that diode died shorted and I could not turn the engine off until I removed the bulb.

Click to view attachment

It does appear that B+ and D- are swapped on your alternator WRT the posted service bulletin. Is that a ground strap connected to the case on the black wire? Did this alternator come with any documentation?

If the black wire is the negative, it should be a much heavier wire as all charging/discharging current will be going through this wire. The gauge of the black ground wire should be the same as the red wire. Here's the Classic Retrofit 175A alternator for my '86's electric AC system. Notice how heavy the black negative wire is.

Click to view attachment

@Spoke thank you for chiming in.

The alternator came with this rebuilt motor. I can try to call the builder and see where he sourced it. I agree on the ground, I use a ground strap similar to the transmission ground, a thick copper beefy wire.

I may have to do some disassembly to see what I can uncover.

Superhawk recommended taking it to a FLAPS and have it tested and see what they hook to and what it reads....might be the best way to verify it given the different labeling.

Hopefully this doesn’t add confusion but it helps illustrate the issue. Internal connections to spade connectors that are attached to the alternator (internal regulator?) circled in red.

From what I can see the rectifier comes as an assembly. I don’t see why they would flip the diode sets but maybe some suppler of rectifiers did.

Since the raw output of the alternator windings is AC, it is the orientation of the diodes that determines how the AC is rectified to DC. Therefore if you follow the polarity stamped into the rectifier plates you to be OK in theory assuming the individual diodes are in the proper plate (that’s a whole different mis-assembly possibility).

Still would recommend having FLAPS or similar bench test to make sure polarity is correct before it goes in vehicle.

Click to view attachment

From this photo and from a closer look at yours I think there is a capacitor (RF noise suppressor) spanning across those two top terminals that are closest together. So doing test #2 I mentioned previously - I think I was wrong - those terminals are probably not the same electrically as I saw in another photo somewhere. In that case it will matter which one has the (61) blue wire connected to negative side as shown in bulletin and as Luke_M mentions.

So I went and dug out my new 75amp alt.
Mine has 3 mounting lugs. 2 on the Neg side and 1 on the Positive side.
If you look at the upper lug on the neg side that's where the Blue wire goes.
See how it's isolated from the base. The lower lug is for the Neg cable (not isolated).
Other side + lug gets a thick red wire that runs to the starter positive lug along with the battery cable. I hope that clears things up for you.

Luke,

Thank you for your effort. If you look at my photo closely, mine has "4" mount lugs versus your 3. That's why this is confusing. As well, mine is opposite yours. If you orient the photos in the same direction, my neg side is opposite yours. But based on how yours is wired, my belief on this alternator is that my lower left side is for the positive / battery. My lower right is the ground, and the upper right would be for the blue wire / dash light and as pictured, it is wired wrong.

At this point, I am going to use this one as a spare, and ultimately will go to an alternator shop and have them definitively test it and tell me. After going to 3 FLAPS and being turned away cause they can't test anything that doesn't have plugs, I bit the bullet and bought a rebuilt alternator identical to yours, to make this painful to the wallet, but painless to attach and get the car running.


I want to thank everyone here. 914 World is a special place. All of you take your time and give your knowledge. It is one of my favorite places to hang out, so from the bottom of my heart, thanks everyone!!

Robert

I will tell you this.. None and I mean none of my local FLAPS would test a 911 alt. I like you went to several FLAPS even after I called ahead and the reply was "no problem".
They have no way of mounting a 911 alt to their test machine. They tried zip ties, straps, you name it. Once the machine started to spin the alt it just fell off the mount.
You would need to find a specialty shop that has the proper equipment to do the test. There was a good alt repair shop around me but they have since closed up shop.
If you think the alt is faulty you may want to get a new unit. Parts Geek has them for just under $350 new. Have you ever done an alt replacement in a 914-6 while the engine is in the car? You'll thanks me later.

I sure miss the old school auto parts stores that I had as a kid.

Crusty old guys with lots of grease under their nails and they spent their time wrenching and drag racing when they weren’t behind the counter. Actually knew things.

I’m sorry you went through that - I think your plan is sound. Glad you’re now working with a known entity that matches the bulletin.

If you would - post an update when you get around to having an alternator shop check out the crazy backward one. Can certainly stand to learn something from that one that is so weird.

After removing the alternator from the fan housing... later model alternators can be
tested as pictured using a drill and an 8mm allen
Another way is to use the V belt fan hub with alloy fan removed.
Rig up an electric motor (polishing / wire wheel ?)with a V belt pulley and test away.

10mm removed to alow for the longer 75 amp alternator.

Now you tell me!!!

Yes, I have since discovered this issue, after purchasing a 75 amp unit, waiting 5 days for it to arrive, getting all excited and discovering it doesn't fit. First I thought, I'll just get longer bolts, but then realized the fan belt would be way off and out of alignment.

I am in the process of returning that alternator, and found a 50 or 55 amp one that has an internal regulator so it should work.

I don't have a shop anywhere that can machine off the fan housing... but I'd rather have the larger alternator. Maybe down the road.

This is so frustrating.

I actually learned this when my 75 amp alt. arrived.
BUT look at post # 24
We both missed that. DOH !

This proves at least 2 things:

1) You don't know, what you don't know, until you see a photo of it and the words mean something.

2) The west coast and the east coast cant read and interpret without a photo...

yes, DOH!!! for sure. I feel like a Homer..

@rgalla9146

So you had to machine down the alternator mount on the engine to install the alternator?

My 930 has one of the Classic Retrofit 150A alternators for electric AC and had to add a spacer because the unit was too thin.

They have this text in their alternator install manual.

The 150A unit is the same length as the early 1965 to 1973 alternators and is a direct fitment for these fan
housings.
Mid year (1974 to 1983) cars with the 70A/75A alternator require the use of an 10mm adapter ring sold
separately.
Late year cars (1984 – 1989) with 90A units require the use of two spacers (10mm and 11mm) to make up
the 21mm offset.

Why not just buy a fan housing that matches the alternator????

Great question Clay.
On my GT project the engine is a 911 SC so the alternator was a perfect match.
The alternator housing has the 930 part number.
On my original 914 6 I wanted the engine to appear stock. It has the housing that
starts with 911 and has the two studs to mount the coil.
I also had a matching spare on hand.
So I used what I already owned. I also have a friendly machinest.

Thank you Spoke and Mlinder

I guess I should've mentioned this earlier too. I ran across the same issue years ago while retrofitting an internal reg alt into a early housing. You'd have to machine the housing like Rory or find a late 2.7/3.0 housing that will work. IIRC The 3.2 is different as well. What I did was purchase a new housing and fan from Vertex Auto. I got the new aluminum 3.0 version and everything fits fine. The pic that I posted is actually my new setup for my 3.4 build. It was not cheap but trying to find a good mag housing was also not cheap. The mag housings crack and can be a pain to fix. Ben welded my brothers 3.0 mag housing and that was sorta a cheap way out. Time will tell how long it'll last.

https://www.vertexauto.com/fans-fan-clutchs...rts-c-7702.aspx

Ok, so thank you everyone for chiming in.

What I learned here was valuable:
1) 50 amp alternators and more powerful ones (70 amp plus) are available
2) If you go more powerful, you may need to check your fan housing and fan for proper depth and fitment. you can either machine down the housing or buy a new one as per the link in one of the posts.
3) They make 50 amp with internal regulators as well.
4) The wiring is fairly standard, but always check.


In the attached, final photo, the replacement alternator I got was different than pictured in the ad. It was laid out similar to the one I had, with the regulator facing down, Pos (+) on the lower left and Neg (-) on the lower right. (Click the photo for orientation correction)

The dash bulb connected to the upper left, and the upper right can be unused or capped off. I had to have the rebuilder provide me with the wiring schematic, which I will save for anyone else who needs it.

I have a spare now as my original wiring turns out to be correctly wired. But without knowledge of the rebuilder and no schematic, getting a new one was the way to go. I will take the original one to an alternator test shop at some point and positively ID the terminals.

Again, thank you to all who helped. I plan to try to get this thing buttoned up in the next 2 weeks. Cheers!Click to view attachment