Originated from a story about an IRA ambush on the SAS near Cappagh in Co Tyrone when one IRA volunteer remarked to another who was firing on the SAS vehicle "Keep her lit!" meaning to continue firing.
Has taken on common usage among Irish republicans especially in the north of Ireland and Co Tyrone.
Has recently received national focus due to a campaign by radio host Hectoc O hEochagain on RTE 2fm
One departing friend to his mates "I'm off lads, keep her lit!"