Your year Atwood uses 120V AC power directly.......
From circuit breaker in AC panel to ON/OFF switch to/thru the set of t-stats and then to terminals on electric element
Depending on which model the t-stats could be attached to electric element or separate (mounted on backside of WH tank)
A GC10A--XX would have a bolt on element with t-stats
A GC10AA-XX would use a screw in element with separate t-stats
Check for AC power coming from circuit breaker (load side screw/wire)
WITH WATER HEATER FULL----With ON/OFF switch ON, check for AC power at terminals on normal t-stat.....then at terminals on ECO (high temp t-stat----should have a button to reset it if tripped).
Then at terminals on electric element.
Tripped CB
Bad On/OFF Switch
Bad set of t-stats (either one)
Bad element
Bad ground connections.
IF ECO has tripped.....then normal t-stat has failed and ECO shutdown heating.
IF water temp is over 130*F/140*F (depending on set point of t-stat) no heating (water needs to cool down below 110*F before reheating cycle can occur.