There is a download for Atwood water heaters in the " Files " drop box , that may help . If your heater has thermal and high limit switches , then power must flow through them to allow the control module to start the spark cycle and open the gas valve.
EDIT: The Files drop box is in the blue bar across the page under the Google search box , left side near your " User CP."
99DSDP 3884, Freightliner, XC, CAT 3126B, 300 HP /ALLISON 3060
2000 Caravan toad, Remco & Blue Ox.