Found it!

After quite a bit of searching I finally found the short circuit in the Emsingen power district.

It's here:

Can't see it? Here's another view:

Still can't see it? How about in this photo?
 

Yep.
I screwed up when I installed the track 9 months ago and didn't pay proper attention to the connecting latches between these two switches. One latch was bent so that it touched the rail when the neighboring switch was pushed down onto the track bed.
This only became a problem a couple weeks ago when I glued down the last track in Emsingen's freight area. I don't glue switches to the roadbed since they have moving parts underneath, so when the loose track seen in the first photo was glued down it pushed down the switch, which pushed down the rail, and made it touch the bent latch.
Ripping out the newly installed track didn't help, because the ends of the switch where tacked down during installation and got some glue, too, so the switch stayed in position. I'm actually glad it stayed put, since a persistent problem is a hell of a lot easier to debug ...


Using the continuity tester in my ampmeter and following the resistance readings, I was able to reduce the problem to the general area of the north switches in Emsingen.

I found the bad latch only after I clamped the leads to the rails and pressed on tracks and switches, as well as lifted them from the roadbed where possible until the beeping stopped.

At that point I could control the beeper by pressing on the joint, and I knew I had a winner.

Fixing it required some gentle force with a screwdriver to bend the latch out of the way.