It's a pretty straight forward project because all you have to do to key the radio is to wire up a momentary switch to short two pins in the PTT connector (bottom right) on the FFCS.
The mating connector for the VIC-3 is a M83723/75W0803N, which is a less common type that is more waterproof than regular Amphenol circular connectors. I bought mine new for too much money, but then I discovered that the "cap" on the VIC-1 crew boxes designed for the Abrams with the PTT port behind the volume control knob is actually not a cap, it's this connector.
For the momentary switch I chose the starter switch out of a MUTT. It's rated for like 100a, which is major overkill, but it's also designed to be stepped on by an angry booted foot, which is what I really care about.
To hold it, I designed a new sheet metal kick panel to replace the one that protects the high-beam switch. It is a bit wider and has mounting holes for the starter switch.
The wires connect to the starter switch with ring terminals.
Augi