Hi BoKo,

Whilst it may somewhat vary a bit depending on whether you are running analogue or digital, if you are using "M", "K" or "C" track, if you have an actual “transformer” (as you say) or other “power source” or what kind of connections you have from the “power source” to the track, there remain a few generalisations, particularly when taken back to the basic principles of analogue :

- "B" stands for “Bahn” (literally “train”) but refers to the “centre rail” (= “puko/studs/active current”). The connecting wire is traditionally coloured red. This carries in analogue a variable voltage controlled by the red controller handle of 7–> 16 ~V with 24 ~V on the reverse red handle action, when compared to the “O” connection voltage of "earth" zero.

- “L” stands for “Licht” ("light") and carries a set voltage of 16 ~V compared to the “O” connection voltage of"earth" zero. It provides “power” to light and other accessory items. The connecting wire is traditionally coloured yellow.

- “O” connects to the two outer rails (“earth/ neutral”/”ground”), it is also the “earth/ neutral”/”ground” for light (L) connections. The connecting wire is traditionally coloured brown.
I am sorry but I have forgotten what “O” stands for in the German language and an internet search leaves me no more wiser (I knew in the past – a current “senior moment”, as esteemed member nevw would say!) I expect there are many fine souls here that will know the answer to that.

- if you are connecting to a standard Märklin “feeder track” connector such as these :

M track (no longer made but much on eBay):



K track :



C track :



then they have the “B” and “O” marked on the connections or have red/brown wires already connected.


- it gets a little more detailed in digital but the concepts are similar.

Please keep asking questions if this leaves you none the wiser


Have fun,

PJ