I would like the wiring to mate the FL-2100 to my Flex 6300.
I used an FL-2100B briefly with my Flex 6500, The main issue is the keying circuit for the FL-2100B. These older amplifiers have voltages on the relay plug NOT designed for modern transceivers like the 6300. I used a miniature 12v relay where the coil was driven by my 6500 (open collector) and the relay contacts were connected to the FL-2100B. No QSK but the Flex is protected.
I did use a FL2100b before I got the SPE 1.3, but I used an ameritron ARB704 between the flex and the amp to protect the flex.