the b battery runs the lamps. from 10-24. The more sets you have to wire the B battery to 24 on the lamps is used based on dimming of lights based on the total number of sets off the power supply.
If you only have 5 or 7 sers then 18 on the b batt is correct..
If you are trying to connect a melco intercom forget how you wired the sets.
Forget what ever prints you have.
The melco has two inputs. One for A battery and one for singnal b battery...
The latch contact makes the switchhook contact in this unit.. If you wire it right you will hear the relay in the intercom unit click. The relay is now looking for audible volatage contacts.
If its a TT intercom you will hear the latch .. It has now made a second connection looking for B battery audible to ring or buzz the station.
