Hi corkster1,
Welcome to the Heartland Owners Forum.
Your Atwood water heater has some common components that are used for both propane and 120V AC operation, as well as some separate. The thermostat and emergency cutoff as well as reset button are all common. So if the propane side works, those are all ok.
The control board is also common and used for both operations, but it's possible the 120V operation could have failed on the board, or on the relay between the board and the electric heating element. But that's a less likely failure scenario.
The switch inside could have a loose wire or a switch failure. Also there's a junction box on the inside front of the water heater where the trailer wires connect to the water heater wires. A bad connection there could be a cause of failure.
One very common cause of failure on the 120V operation is that the electric heating element can be burned out if operated when no water is in the tank. It's takes longer to do this on Atwood units than on Suburban units, but it's possible.
To determine where the problem lies, I think you'd want to measure voltage at several points on the control board. That would tell you if 120V AC is present and you may be able to verify operation of the relay the board fires to connect 120V AC to the heating element.
You can find more help and wiring info in the service manual located in
this folder.