**** Note On many Lenz Decoders ANY change you make does not take effect until after you remove and restore power to the decoder. You can do this by rebooting your DCC System or tipping the locomotive to break rail contact.
FYI - The MTC21 was never intended to be a general DCC decoder plug format.
The letters of MTC = Marklin Trix Connector. A proprietary connector that supported DCC on a specific locomotives being made between these two companies.
The problem is the socket grew beyond what it original intent was and got adopted by other locomotive manufacture before any real standards could be defined for it. Hence the multiple versions.