Troubleshooting Failure to Shut Down--what a puzzle

And so Adam returns.  

Uli--good catch.  Wrong pin.  The pin directly across from the ignition ground (cf 74-00-00, p 29, 15) is a spark plug ground.  So of course this pin (15 in the same illustration) was always grounded!  Whoops.  The correct pin connected to the grounding switch (7) grounded  properly at the correct switch positions.  Switch grounds were solid.  Having sorted out this mistake it was nice having 15 as a reference point when I was checking the ignition switch. 

I reassembled the connectors and fired up the engine for a ten minute run to warm the oil.  The engine shut down normally.  Of course.  And it continues to function normally.  So I suspect the cause was a poor electrical connection, perhaps one of the grounding pins was dirty or dislodged.  

The time, effort, and thought maxim certainly applies.

Hello Adam, I don´t know whether You have already solved this issue. I had same symptoms, headache, investigation. Today I tried to check whether the Ducati ignition boxes got Ground. As I tried to unlock and disconnect the white connector, the cable just broke apart. The Ducati boxes have some protective plastic coating on the wires, when it hardens, it can actually act as a knife and the engine shaking is enough for cutting the old wires. I have a y. 2003  912 ULS, without overload clutch. After I made a new connector, the engine stopped immediately. Long story short, my advice is to check the wires coming directly from ducati ignition boxes.