I had my starter on a 240D go.
No problem, get a "new" rebuilt Bosch and snake it up in there for a workout and attach it.
Go to attach the battery connections and the starter fires!
Fortunately it's in neutral and doesn't take off.
Check the ignition...it's off and the key isn't even in it.
Switched the connections on the starter just to see if I screwed that up...but no power goes through in that configuration.

So what did I do to cause this "open take off mode" and how do I rectify it?
Thanks!

P.S. The only other thing I did was have the key in during the starter removal and replacement so that I could crank the wheels to the right so I could snake the starter in from below...but then removed the key.