I have an Atwood G6A-8E
Check for a bad fuse in panel first, then with a 12 volt test light or multimeter, check for power in to switch, as well as out when in on position if it's easy to get to. If not, turn switch on and test for voltage at brown wire to thermostat terminal, that comes from inside at back of water heater from switch inside. If it has cut-out switch in plastic sleeve attached, be sure to check for power on both ends of that cut-out switch. If power only in but not out, replace it. As I said,that brown wire comes from switch, so if no power to it, check at switch. The other brown wire goes back to connector on ignition board. If power is there, turn switch off, take an eraser on end of a pencil and rub contacts on ignition board/module to clean them off, as well as spray electrical cleaner on contacts of connector to make sure you have a good connection. Check all ground connections as well, and if you have 12 volts at brown wire to connector on ignition board but still no spark, replace ignition board/module.