Generally, the gas side of the water heater, if it is a DSI (DirectSparkIgnition) model, will have a red light on until it fires and stays on.
Otherwise, a red light next to a switch usually indicates power is going to...somewhere?
Wish I could be more help.
2016 Tiffin 40 QBH
2015 38RSSA, traded
2005 TK3 #1869, 10 yrs of memories,
2017 F450 KR--one more Ford is it
2009 F450 4x4-died; 2010 F450-retired