The micro switch that is on the bottom of the shifter, what passes current to it? Is it the brake pedal switch, or the button on top of the shifter? In other words, how does this micro switch work? I think it passes current that locks the shifter via solenoid. I'm wondering how it all works.

The micro switch has grounding current of .02 volts. Its purpose is to send a ground signal to the shift lock solenoid. The contact gets worn and needs replacement or adjustment of the little reed that activates the switch. Its tested by using an ohm meter to ground and testing through the switch. Pauli

On the 850 there is a mechanical lock also - perhaps yours is the same.

Are you having trouble with it?

Two years ago, I had a lot of trouble getting out of park. I checked the switches and they were working OK.

There is a rod in the shift lever that pushes down to move a lock near the bottom of the shifter when you pull the button on the front of the shifter.

I took the console apart to observe its action - the rod did not go down far enough to unlock the shifter.

Since the rod looked undamaged, I reasoned that the shifter had moved up. I had read on BB that the shifter was just pressed on,

I gave the shift lever a couple of downward smacks with the palm of my hand - problem solved.
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'96 855R,'64 PV544 driver, '67 P1800 basket case, '95 855, '95 854, the first three are mine, heh, heh, 485,000 miles put on 9 bricks

The brake light switch sends voltage to the shift lock solenoid which withdraws a pin and allows the shifter to come out of park.