http://www.ft86club.com/forums/showthread.php?t=114212
http://www.ft86club.com/forums/showthread.php?t=95444
In a nutshell, it's an externally amplified circuit that is powered by the radio. Aftermarket radios do not operate in this way. Many have tried, but all have agreed that in the rare case you get signal to the headunit, it's garbage compared to just running an aftermarket mic.