Welcome to a fun weekend!
1. Disconnect the battery!
2. You need to remove the speedometer and instrument cluster and if you haven't done this before read this first:
http://www.sl113.org/wiki/Electrical/DashboardInstruments#DashboardRemovalOr:
http://www.sl113.org/forums/index.php?topic=6072.03. Remove the cover under the instrument panel in the foot well.
4. Check whether the 3 screws from the back of the switch (7) [see picture for numbering] are tight. If not your problem could be the rotating switch not making good contacts. Otherwise remove the screws with a short stubby screw driver and remove the switch with all the wiring and inspect it.
It should not matter whether you have the 1st or 2nd version of the lock mechanism for this procedure. However, if the rotating switch (7) is OK and you need to remove the cylinder (5) you must know which one you have.
If you
cannot pull out the key in
garage position "1" then you have the 2nd version.
All of this is described in the BBB on pages 46-8.