The thermostat connects to the furnace
with two wires. Connect the ends together, which is what the thermostat would do, and the furnace
should come on. Shortly after that it should ignite. If it fails to ignite it will turn off. Then you have a problem. On mine I found a cold solder joint on the control board. The common issue is a bad sail switch.
Once repaired, my Atwood works quite well. The Atwood thermostat is not of very good quality but since I use it manually, as a on off switch, I haven't bother replacing it.