1969 911E - Alternator Light

I just picked up my first longhood and couldn’t be more excited. However,the red alternator light came on today and I’m hoping someone can help. I was driving the car this morning with no light and at a stop light my idle dipped to ~800 and the light flickered. It went out as I increased the revs.

It eventually came back on a few minutes later and didn’t go out. After some searching, I’ve done a few things that hopefully help to diagnose.

1. The light does not stay on when I turn the ignition off.
2. The light does come on in the accessory position before cranking.
3. The light stays on with seemingly consistent brightness throughout the rev range.
4. Battery voltage when off: 12.38V
5. Battery voltage at idle and at 3,000 rpm: 12.06V

Finally, here’s a picture of what I’m dealing with - not sure what if any hacks have been made. Sincerely appreciate any help.

Attachment 596753

Battery should be about 12.6 to 12.7 when new and fully charged. Alternator should be at least 13.5 when running at idle and above.

With 12.06 volts when running, you are continuously discharging the battery and the engine will eventually quit in the not too distant future.

The red light is doing what it is supposed to do-warn you that the voltage is too low.

Almost certainly, the voltage regulator has problems or the alternator has failed. Do not disconnect the battery while running the engine as the alternator can be damaged

Congrats on your new long hood.

Your measured voltage at 3000rpm is abnormally low, should be about 14V or so. So your alternator is not charging properly or your voltage regulator could be faulty. There is a test to differentiate the two but I am not smart enough to tell you how to do it in a safe manner, it involves some risk if not done properly...On a new to me old car with little history to go on I would address both the alternator and the regulator

Your voltage regulator is a replacement and the wires have been spliced, one possible reason is a motorola type harness was there originally (common for 1969) and someone spliced in a bosch type plug for the replacement regulator.

One solution would be to remove the alternator, take it to a shop for testing and rebuild. Replacement alternators with built in regulators are available, they require some minor wiring modifications and some do not like to place the regulator in the hot environment on top of the engine.

It sucks to just replace stuff, but a new solid state regulator is not too expensive.

Thank you both very much for your insightful responses. I suppose, rather than perform a risky test, I’ll just replace the Voltage Regulator first. Is an exact replacement of this part the right direction? I see many kinds are available…

https://www.stoddard.com/90160320602-sic.html

Thank you again!

First thing I would do is ultra clean and shine every wire connection.
One by one
Including getting to to the wires behind the alternator.
And especially every ground.

And see where that effort leads.

Thank you - will do some cleaning up. Should I be focused on the area shown above (driver’s side of engine bay) or are there other areas that could potentially contribute?

Start with the battery, clean both posts/terminals and the ground attachment to the body. Your car had two batteries originally, so lots of em have been modified by now, some better than others. Make sure all looks well in the front trunk battery area.
Next major ground is front right transmission to body. There is a ground stud behind the fuel filter seen in your photo above with perhaps 5-10 brown wires attached. Also, you could clean the terminal at the very left of you photo, the red/white stripe wire probably goes to your alternator. Make sure your voltage regulator terminals are clean and the plug firmly seated. Your VR looks just like your stoddard pic so might guess it is not too very old.
There is a ground straps and several significant connections on the back of the alternator, but obviously you have to remove the alternator to get to them. At that point get the alternator tested.
Of course, your VOM probably has a setting to allow you to test the continuity of all these wires if you wish.

https://patrickmotorsports.com/produ...a53cacca&_ss=r

While I find the time to check connections and wait for a new VR to show up, I thought I’d post a pic of the driver’s side battery box. Looks particularly messy with some aftermarket additions (those relays on the bottom left?? Also this fuse?). Not sure if of any relevance to my issue but figured more info is better than less.

Attachment 596911

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I would remove the alternator and voltage regulator and take them to an alternator/ starter shop to have them tested. Takes about an hour but you need the tool to remove the fan belt. Check the articles from the 101 projects book on Pelican Parts (online) for details.

Edit, this one:
https://www.pelicanparts.com/techart...eplacement.htm

I have also a 69´s 911E.

Check this :
https://www.early911sregistry.org/fo...-compatibility

You have to check if your alternator is a SEV Motorola/Marchal or a Bosch because the regulator is different.

Attachment 596936

Here is what yours should look like. The only good thing I see is what appear to be headlight relays, although poorly wired in.

Thanks all - hopefully we are getting somewhere.

I pulled the fan, housing, and alternator tonight and the alternator has seen better days, though that doesn't mean much. Any idea which one this is? I'd rather not separate the housing and fan yet, but may be headed that direction.

My wiring:

Big red wire with white stripe connected to B+
Small red wire connected to +61
Black wire with tape labeled "DF" connected to DF
Brown wire connected to D-
Ground strap connected to case

There also did not appear to be an inner air guide - were these early cars equipped with them?

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You can take it to be tested, and that’s a good idea.

And there’s a pretty good chance, you just clean it up and it will work.
Do your best to check and fix bad wires, and wires that don’t look like they’ll last much longer.

Pulled the alternator out of the housing and took the fan off. No markings other than this tag from a rebuilder. Did not see anything that would indicate Bosch or SEV/Motorola, etc.

Going to take it to a local shop for testing.

Is this alternator worth rebuilding if it ends up being bad?

Attachment 596951

Those look like fine threads on the shaft, that would make it a Marchal. And the Bosch alternator usually had a riveted on I.D. tag.

This is what you should have on your 69's 911E :

Attachment 596952

The big red/white on B+ goes to the batteries.
The red on D+/61 goes to the regulator.
The brown on D- goes to the regulator.
The black goes also to the regulator.
The grey is a ground going to the engine top case.

The regulator you can find for a SEV Marchal or Motorola looks like that :

Attachment 596953

As you can see the little red wire coming from the alternator is jumped with a blue wire that goes to the dashboard red light.

The good wiring is here :

Attachment 596954

My alternator was in a very bad shape but still working (I replaced it of course) !

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Quote:

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Originally Posted by edmayo

Those look like fine threads on the shaft, that would make it a Marchal. And the Bosch alternator usually had a riveted on I.D. tag.

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If it is indeed a Motorola type alternator, and someone has spliced in the three prong connector to accept a Bosch style VR, then perhaps that is my problem.

Anyone know if I can simply add the Bosch style alternator since the VR harness has already been adapted? Or more complicated? Should I still have this alternator tested/fixed?

Here is a better photo of the VR harness that has been hacked to accept a Bosch style VR.

Attachment 596963

After a bit more research, I suspect this is my problem:

A prior owner was having charging issues and either couldn't find a SEV/Motorala type VR or thought the Bosch-style VR was superior and modified the harness to accept it. However, they did not to match the VR with the alternator. Thus, we now have a Bosch VR combined with a Motorola alternator, and I have read that the Bosch VR has a lower set point than the Motorola alternator requires, so the battery is slowly discharging over time. This would explain why there was no light when the car was fresh off a battery tender, but once the battery slowly drained enough, the light came on.

My proposed solution is to install a refurbished Bosch alternator. I believe the wiring is all correct for me to swap it in as long as I match the wiring schematic posted above.

Does anyone see any flaws in this logic/approach?

You may have this sticker in your engine bay !

Attachment 596968

Your approach with a new Bosch alternator seems reasonable. Lots frayed wires visible in your pics where the terminals are crimped on, as is common on our 50+ year old cars. Your wires will probably work ok, but if you really want to clean it up, check out kroonwireharnesses.com. Often the wires have enough slack to allow for removing the suspect terminal and last cm of bad wire and crimp on a new terminal. It can at times be deceptive, as the old copper wiring is sometimes brittle. Or just about all the various harnesses are available in high quality replacements..

Thank you @garycox and others for your contributions to this thread, and to all for the countless threads I've visited and researched over the last few days. As soon as the parts arrive, I'll chime back in with the outcome.

I don't think the charging light works as you described. Either the alternator is delivering power to the battery and it is charging, and the light goes out; or it is not. It doesn't make sense that the light would start to illuminate as the battery is losing charge. Either way, replacing the voltage regulator with the correct one, and checking/rebuilding the alternator will most likely solve the issue.

Installed the refurbished Bosch alternator (with matching Bosch-style VR) and we now have 13.6V at 2k rpm and NO LIGHT. Thank you all for your contributions to this thread.

Even tho it is working you still need to start addressing wiring at the battery (batteries) For example, the battery ground connections,,,where are they grounded at? the proper ground point is that wing nut just above the battery, not three feet away as your picture seems to show.

A prior owner wired in a kill switch under the dash, hence the ground relocation.

Based on the records I have, people have been chasing down charging issues since 1971. Hopefully, this solution remedies it for good.

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