This is a 10-pin to 7-pin adapter cable for connecting a the 60653 Mobile Station, the 60652 Mobile Station, and the 66950 Trix Mobile Station to the 60125 Terminal and a 3rd Mobile Station to the 60213-60215 Central Stations.
This cable can still be used to connect a second 60652 Mobile Station to the 24088 feeder track or to the 60115 Connector Box (H0) or 60111 Connector Box (Märklin 1).