I first ran into this difference years ago when trying to use my MD-1 Desk Microphone with a newly acquired (at the time) FT-920 Transceiver. If you look at the schematic of, for instance, the MD-1 compared to the MD-100 you can see the difference. BUT, note also that there was a later version of the MD-1 that had the updated wiring. Seems, if I recall correctly, that there was an MD-1b8 that I had but that the later version, MD-1c8, had that wiring updated. I have since updated both MD-1¡¯s that I have here to ¡°c8 status.¡± If you cannot find the details, let me know and I can do some digging here to help you.