Oskar Vierling BSW-Variometer power connections

I just got one of these antique varios from New Zealand, no
less! Don't worry, I got an excellent price

It looks like there are only four connections to hook
up. "A" is probably ram air. "S" is probably static.
Then there are two power wires, unmarked (uh oh).

The tape on the wires says "12 volt power supply"
but no idea which is + or ground.

There's an empty instrument hole in the rear of the Blanik and
it's just BEGGING for an audio vario...
Is the top wire "+" or ground? Anybody ever had one of these?