Finally got my SH AIS VHF radio. Setting up now. I need advise. I'm connecting an old Garmin 12XL gps to the radio for AIS to work. There are +,-,R and T pins on the 12XL. Should I be connecting the T to NMEA In(+) of radio? What about the NMEA In(-) ? Do I wire the gps "-" , which is the 12V negative, to NMEA In(-) ?