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Dave at Pelican Parts Dave at Pelican Parts is offline
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OK, first things first: I just barely know jack squat about Bimmers--and less about the 80s 3-series! So anything I can tell you will be pretty much from a "well it looks like the diagrams say" perspective.

With that said, the second post first.
It looks like the diagram is saying that the two 87 pins on the main relay are hooked together inside the relay, so they should be electrically identical. You're showing the same thing on both (0V) which seems to say they are OK. What the relay should do is to bridge together the 30 pin with the two 87 pins when there is voltage across the 85/86 pins. Since 86 (? diagram is fuzzy) goes straight to the battery, you need to check that 85 gets grounded when the key is on.

First diagram:
C and 50 are electrically the same, since they are connected inside the switch. (At least, according to the diagram.) And when you turn the switch to "start" only, both of those should be bridged to 30 (and to C1, which is connected to 30 inside the switch).

So now you need to figure out which wires correspond to what in the diagram. I think it's pretty safe to say that your red wire is the same as the red wire in the diagram, as it is the fattest wire in both. (Labeled with a 4mm-diameter conductor on the diagram, the others are 2.5mm or less.) And that makes sense, as it's the power supply for the whole switch. After that, guessing gets hazardous.

OK, so you've checked each wire in each key position. The results don't seem to make a whole lot of sense, but this switch has a couple more wires than the one in the diagrams. (That's what happens when one book covers many model years, sad to say.) I would double-check those tests, as at least one wire should connect to 30 at all times but "off". If the tests give the same results, then I think the switch is the most likely culprit. It only makes sense that some things are powered with in "ACC", and others only when the key is in "run".

.... But as I said, I'm not very up on the BMW side of things ... Hopefully someone with direct experience can chime in here.

--DD
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