Thanks for your reply. I will do that first thing in the morning. (I want to do it now, but it's dark, cold, and I have been up 24 hours straight already -- a sure recipe for mistakes and accidents!)
Prior to my surgery on all alien wires and relays in the car, the device was connected to the alarm LED and/or the alarm cutoff switch. Perhaps cutting the connecting wire caused the switch to permanently set itself to "disable?" And, if it is indeed a kill switch, it seems to work when the battery is disconnected -- which I did in a vain attempt to "reboot" the system.
The MB Tech did notice the device when he tried to manually start the car from the switch you mentioned. Apparently, he neglected to consider that the device was still part of the circuit and, if active, would continue prevent the started from cranking.
Two things I forgot to mention:
I think I can hear a clicking/clanking sound when I try to start -- is that the starter solenoid?
Also, when I try to start, the fuel pumps keep hissing. Is that normal when the starter does not engage?
Thanks again for your help. I'll let you know tomorrow how it goes.