609,
You've got an early ESU decoder (lokpilot) or even the early Roco decoders with an 8 pin plug.
If your other loco has the same digital socket all you have to do is take this one out by lifting it off and press it in into the other loco digital circuit board.

there are 2 things you have to be aware off:

a.) the decoder plug has to go into the position with the red wire facing a star on the circuit board
b.) make sure your other loco has a digital circuit board and not an analog.

having an 8 pin plug or a 21 pin circuitboard, this is the way to go and the advantages are, you don't have to do any extra soldering. the only wire which is not part of the 8 pin plug is your violet wire (Aux 2) if this has been used you have to unsolder it and see if you can use it on the other loco. if you can show us the other loco I will be able to tell you if its suitable. make sure you tell me the item number and who has manufactured it.

regards.,

John