I just re-read your post.

It sounds starter related to me. If you find this is happening again, turn the key a little closer to the first detent.
Do you have a lot of keys on your ring?

I can't think of a reason it would squeal in P and N. I think there's an idle speed increase(decrease?) for shifting into drive or park or one of the two.
There's a lock in P, but there's essentially no load in N. Maybe something got into your bellhousing and only makes noise if it winds up in the wrong spot.
Check your plastic bellhousing screens. Mine had disappeared after all these years, but a junkyard one was like $1.

You should grab (or phone) someone to come hold the brakes the next time this happens, then start listening around and poking at things with a wooden stick.

Are you sure the belts are all tight? Testing the timing will help you determine if the harmonic balancer is intact. You can rent one for a 100% refundable deposit at Kragen, Autozone, and maybe some other places if you don't own one.

We can't come up with a ton of new ideas without new information or observations.
I am really inclined to think your harmonic balancer is failed/ing. It failing can cause the belts to squeal and your alternator to stop spinning - and therefore stop making juice.

Good Luck
--
1990 740 Turbo, on its way to stock specs, maybe beyond

Hi,
Thanks for the Answers!
The Choice of my wording may have been misleading, its That It wasnt a squeal, it was more a metallic Clanncking Scrreeech sound... definitively metal against metal and followed by a screech-squeal...AND CERTAIN ON_OFF_SWITCHING of this sound with the Tranny Positions P and N, NO sounds otherwise, while the lights etc did not work the whole time. Since this happend the car worked normally for 3 day now... So very intermittend. I just need to find it and fix it before it gets me way out somewhere at 40 below......
Could be Starter against flywheel !!! or maybe the Locking devive from the Park Position???
Came from there, too!
Regards,
Lars

Hi Lars,

I can't see how a slipping harmonic balancer can kill the lights etc and then have it
start up normally with everything working?

If you lost headlights and then they come on again normally, I'd wonder about ratty
battery cables and cable ends.

The screaming belt thing could be a harmonic balancer and unrelated to the dead lights and electric?

Get a meter on your battery terminals and see if you get 14VDC with the engine running.

There's some rubber bushings on the alternator that go west and cause misalignment.

Doublecheck the piggy back plus wire at the battery- If you lose that you lose your
charging. (But that doesn't seem to be whats wrong)

Post back, Bill

The symptoms sound like something (the headlights?) is drawing an unusually high current and putting such a load on the alternator to make the belt slip and squeal. I would look for something like the headlight wiring shorting somewhere.

I like the harmonic balancer, though I haven't had one fail for me.

The key (part of the lock mechanism) can stick in the start position, especially with a heavy key ring, and make the starter stay engaged. I couldn't drive my car like that though, it idled at about 400rpm and had the SRS light on.

Have you checked the transmission fluid, just for kicks?

Good Luck!
--
1990 740 Turbo, on its way to stock specs, maybe beyond

Just a WAG but perhaps a possibility. The pulley on the crankshaft (harmonic balancer) is of two piece construction that has a rubber piece between the two pieces. It is not unusual for it to separate enough for one to slide over the other. That would account for the squeal.

It can slip enough sometimes to render the alternator useless and even cause overheating.

I am unable to assign reason for all of the other symptoms, but I would check the harmonic balancer.

Randy