The circuit board has been developed for Märklin Mikado locomotives, such as item 37970, and fits exactly in place of the original decoder.
For decoders with a 21MTC interface.

This adapter is also suitable for sound decoders.
The Aux3 and Aux4 connections are reinforced on the circuit board and are brought out to pads. The function of these connections depends on the decoder used.

The locomotive’s wires are soldered on as shown in the instructions.

Connections for the loudspeaker are provided.
Supplied without a decoder.