When starting the hot water heater on gas using the 12VDC rocker panel switch, per the Atwood owner manual found here:
"The next step is the direct spark ignition system. For a period of 6-8 seconds the circuit board will send voltage to both the gas solenoid valve and the electrodes. If ignition does not occur, the board goes into a lock-out condition and the non-ignition light illuminated at the ON/OFF switch."
So the light at the switch should normally be off, unless the unit has failed to light when requested.
When running on 110VAC, there is no indication other than that the switch has been turned on, UNLESS someone has possibly installed an inside switch with a power light on it.
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