Thank you very much, Len.  That makes sense.  I'll be running DCC so the missing part won't matter.  Very annoying though that Bachmann did not include any instructions for part; what it is or how to install it.  I guess they haven't changed all that much from the old days.

Best regards, 
Carl

New member here.  I just received two Bachmann GP9 diesel locomotives (DCC On Board, Item 62808) that I purchased on sale from an on-line dealer. 
One of the locos has a small 6-pin PC board, with only four pins, in a plastic bag taped to the outside of the inner clear packaging.  The second loco does not have this small PC board in the box.  There is nothing in the instructions referring to the is PC board to what to do with it.  Is this supposed to be there?   If so, what should I do with it?  Is it missing from the second loco's packaging?

Any help would be appreciated.

Carl