Hi Rupy,

In the digital era, there is no ”AC or DC”. Everything runs on digital power - a ”kind of” AC power - where DCC, Motorola and Mfx protocols can coexist on the layout. Newer Märklin engines come with decoders enabled for all three protocols. The Z21 can control DCC and Motorola decoders, and the decoder in your Fleischmann engine probably supports at least one of these protocols.

The major European model train suppliers produce both 2- and 3-rail engines these days.

Generally Fleischmann locos will be designed to run on 2 rail track. If you are using Marklin 3 rail track your Fleischmann loco should have a pickup shoe fitted to the centre of the loco's front bogie for it to be able to run (I reread your first post and see you say it is designed for AC / 3 rail use).

The track output from your Z21 (you don't say whether it is a black or white Z21) connects to the B (red) and 0 (brown) connections on the Marklin track. If the loco supports the DCC protocol use that, if not use the MM protocol.