Picture is TOO LARGE...makes it hard to follow info etc
THAT is an Atwood GC10A-4E water heater.....electric.gas combo and uses a Common DC Fused source for controls/functions
Fused DC goes to the On/Off Switches (inside RV) then from switches DC goes to circuit board (Electric/White wire & Gas/Orange wire)
DC then goes to/thru T-stat thru Thermal Fuse (inside the clear tubing---blows at 190*F if flame blows back out of combustion chamber---must replace if blown) and back to circuit board (Brown wires)
*thermal fuse can be removed...wire connected to t-stat to 'TEMPORARILY' operate water heater
When DC comes back via brown wire then Circuit Board sends DC to ECO/Gas Valve......
On Gas it would be FULL DC Voltage to open gas valve and energize Spark Electrode (high voltage spark)
On Electric it would be just a few millivolts so that ECO (Energy Cut Off/Hi Temp T-stat) is incorporated into control loop
On Gas Spark electrode FIRES (Click, Click, Click) and ignites propane from gas valve provided propane is available, orifice/burner are clean and spark electrode wire/connections are good)
On Electric DC is sent from Circuit Board to DC Relay which closes and allows 120VAC to go to element provided AC Circuit Breaker is not tripped, wiring at DC Relay is not bad and element is good (energizing w/o water will burn element out in seconds/minutes)
2A fuse on circuit board protects DC circuits on board...if blown/no functions (and probably a shorted circuit board)
Got a Voltmeter...know how to use it....trace the DC circuits from on/off switches to circuit board and components.
Here is the wiring diagram to follow circuits
