The squib test checks continuity THROUGH the squibs and gives you a quick clue about the status of the squib circuit. If there is no or too low test current, too high resistance in the firing element etc the test will fail.
The low pressure light indicates low pressure in the fire ext agent bottle, but to be sure, look at the gauge on the bottle.
I guess a detonated squib will break the firing element and cause an open circuit, but I'm not sure.
Refering to you question about bottle discharge;
The low pressure light is the only way for the pilots to know whether the fire agent has been released or not. Then hopefully the fire warning will go out.
Last edited by Wmn; 5th Feb 2012 at 22:57.