Just before the contest next weekend I decided to use my old FT-817 as a driver for my DB6NT 13 cm transverter. As all other TRV's it needs a low PTT contact to enter TX mode. The FT817 has a TX-GND on the ACC socket but no specifications.
The TX GND uses a 2SD2211 transistor driven by a 10 k resistor, so the theoretical maximum current of 1.6 A is never achieved. Good news, you can't rape the poor little device. The bad news is you can barely switch 100 mA. So forget about switching those huge RK-400 or CX-520 coaxial relays.
I hope this info is of some help...