Does it look like this one........
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That is an Atwood gas only with ignitor.
12V DC power (from DC Dist Center....fused) goes to ON/OFF Switch. From switch it goes to T-stat (brown wire) thru T-stat to module. From module to ECO (red wire) thru ECO to gas valve to ground. High voltage comes from module to ignitor (until main flame lights off)
SO....with On/OFF switch ON you should have 12V DC to t-stat (brown wire). No 12V DC then bad fuse, bad fuse connection, bad switch etc.
Just need to follow the 12V DC and find where it stops