going into wiring color codes and conventions, all you need to know is to re-connect the second line jack to match the live jack.
Open circuit voltage between conductors of an idle pair (as yet un-disconnected by Telco) of telephone conductors can range from 50 to 60 volts DC. The ringing voltage can reach 90 volts AC. Therefore, always work carefully with insulated tools and stay clear of bare terminals and grounded surfaces. Take the phone off the hook on your primary line, in which case, the DC voltage will drop and their should be no AC ringing voltage delivered.