I assume you are speaking of the red light on the propane on/off switch.
This light is more of a fault indicator than anything.
It should light momentarily when one switches on the propane system and then go dark. If the water heater lights and is burning, the lamp will stay off.
If the water heater fails to ignite or quits burning(perhaps runs out of propane) at some point before the water gets hot, it will light to indicate a fault.
It has nothing to do with the electric operation of the water heater.
Jeff & Cindy
'09 27FB Flying Cloud
'91 350 LE MH