1 audio transmission
2 audio receiver
3 ground
4 terminal connected to ground. It can be isolated
by cutting W1 jumper (W5 for FT11U/D).
The relay contact, normally open, is connected
between terminals 4 and 5.
5 lock release (max 1A)
6 intercom call input (12Vac-150mA)
7 relay contact...