So, it is very much of an intermittent sort of problem, sometime it is like this(on the video), sometimes it is alright, and what i have noticed yesterday, the light in the car(dashboard and the other bulbs flicker, and turning on or off the any electrical stuff in the car causes rpms go down significantly and than fluctuates. Also i noticed it drains the battery(battery is new, 8 months old), i'm still able to start the car in the morning, but i can feel that battery doesn't have much of juice, then i drive during the day, battery again is juicy for starting. During the holidays, i haven't started the car for 2 days, it drained the battery completely, had to jump start it. Also, i bought a new Voltage regulator(KAE) original, and on the third day after i installed it, i noticed that, when i turn off the engine and pull the key out, the check engine light stays on as if in the 1st key position and i can hear the idle control valve clicking and some other electronic works under the hood. I switched the voltage regulator back to old one and that problem was fixed, but i think, that there is some short or something, that killed it, I don't think it died itself in 3 days for no reason(both fuses were not burnt on regulator, what's weird).(1) So it looks like pin 1 is connected to the ignition coil low voltage side from your picture. Perhaps it is providing a virtual ground (or battery voltage) when you take measurements. Maybe that's why it sort of works.
(2) Some meters will give you garbage if you reverse connect the leads. Mine does. Even though it is a very good meter. Though yours seem to work that way I would not trust it 100%, always go ground to signal and do the math. Safer that way.
I also have an '89 M103. I can take some measurements and collaborate your results and connections. Not for a few days though, it is raining heavily here, and will do so for a week or so.
Seems you need to hit the books anyway. Good luck with the finals.....
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