You mean the oxygen panel lights, near seatbelt sign switch? Thats not a pressure warning lights. That lights says that oxygen system is charged, so it can be used if necessary.
They should illuminate above 14 000 ft, system works automatically.

There is no pressure warning light in CS 707-300.

As for pressurization:
1 - set airfield elevation.
2 - load pax n cargo
3 - close doors
4 - takeoff
5 - clear flaps
6 - do after takeoff checklist, and there is item air cond & press.
At that moment you set pressure altitude for cabin. 6 000- 8 000 ft, and then monitor differential pressure. it should not reach limits of 9.5 or so.

For landing you operate it so your cabin pressure alt be lower then altitude you flying. pressure inside cabin must be greater than outside pressure, so doors be pushed outwards for more sealing.

Thats how i doing it, but its good to know real thing from real pilots!