Initially, I had to screw and unscrew the red and black/brown wire to the rolling test stand. It can be quite frustrating having to do that everytime I want to use it. Somewhere I saw the use of a piece of C-track as an intermediate connector between the mobile station and the test stand. The idea was to allow the Märklin wire connectors from mobile station track box to the test stand via this intermediate track (see below)

Before

I finally found the male connectors (see the gold pieces) at a local electronic store. This allows me to connect the test stand to the mobile station track box WITHOUT the C-track.

After