1) There's no resistor in the door lock, only a contact switch. Does it help if you force the key against the stop?

2) Open the sunroof 1/3 to 1/2 way. Pull down the leading edge of the ceiling liner on the sunroof panel. You're dislodging 4 or 5 friction pins. When the forward edge is released, pull it forward as much as you can then while holding the liner slide the sunroof all the way open. I'm not sure if there's a better way to do this but I lay a clean towel over the roof section between the windshield and sunroof opening and pull the liner up and out. You can see most of the sunroof mechanism without taking things apart that have to be aligned on installation. When you put back the liner, note the 2 ski clips (they look like skis) on the trailing edge. Make sure they're oriented so the tilt function works properly.

Sixto
87 300D