Remove the cover from the burner area and have someone attempt to light the ref. You should see or rear the igniter sparking against the burner.
If you do not have a spark you may have a bad board or coil.
If you are see or hearing a spark and the burner still will not light you may have air in the gas line and the pilot valve can not bleed it off. Crack the gas line at the ref. just long enough to smell gas and tighten it down and try again.
If you have gas and spark but the resulting flame is poor in shape or colored mostly yellow rather than blue you most likely have a spider in the burner tube. Remover the burner tube and clean it.
Odds are it is one of the last 2 comments as apposed to a bad electrical component.
WBCCI 12156 AIR 3144 WACHUNG TAC NJ6
2004 Excursion 4x4
1991 34 ft. Excella +220,000 miles, new laminated flooring, new upholstery, new 3200 lbs axles