What voltage? The only thing your wired remote of any kind should connect to the tuner module are pasive resistors without suplying any power. Those resistors and that 22kOhm thing make up a voltage divider (for internal 5V supply), and ADC measures voltage between them (0-5V).

So, either I missunderstood your post, or you missunderstood the wired remote description on riocar.org

Aha, you could provide ADC with 0-5V voltage directly, but I guess you would have to dissect your tuner then and disconect that pull-up 22k internal resistor.