Here's what you would be seeing if you removed the intake manifold to access it from above. This is my 2001 3.0i.

The wires with the corrugated conduit with red ends go to the solenoid there, which is parallel to the actual starter, seen immediately inboard from the solenoid. The red end at about 11 o'clock comes directly from the B+ jump port in the engine bay. The red end at 9 o'clock goes on and ends at the alternator.

The two much thinner wires there that go to the solenoid just control the solenoid, which of course closes the circuit for the starter and engages the gear with the flywheel.

In case you're not used to seeing an engine bay looking like that, the aluminum block that says BMW, and has blue and yellow masking tape on top, is the 6 cylinder engine block, head removed, masking tape covering the open cylinders.

I believe that although it is visible and reachable (e.g., if you just needed to tap off the B+ there) from below, that removal or any actual work on it "needs" to be done from above.

Attachment 78657

Attachment 78658

Thanks for that! I've had the intake off and the bottom plate as well and I remember seeing it, so you've refreshed my memory on when I saw it.

Maybe one interesting note that may or may not help.

I took those main fuses out that are on top of the fuse box. The 60,50,60 that are on that powered steel bar on the very top. I checked those and didn't see any issues, but forgot to put them back in. When I hooked the battery back up, with those fuses out, everything lit up and came on, radio, rear blower (front blower is unplugged so it may or may not have been powered), the climate control lights, etc, were all on. Of course the car wouldn't start with those fuses out, but it made me think that whatever those 3 are powering, the problem isn't with any of those.