Gotcha!  Unless I am misunderstanding something else, this looks like an oversight in Deere's engineering of the extension harness.  It looks like the extension would work with the "regular" front harness but not the CAN front harness.  However, the document I have clearly shows using the same extension for either type.  All you need is the just to extend the 3-wire connector for the master switch, isn't it?  Looks like PF81139 11 meter harness is the only choice.