By the looks of pics you have an Atwood WH
Backside of water heater:
Check that valving is set up for WH use
Cold inlet valve OPEN/Bypass valve Closed/Hot outlet valve OPEN (unless mfg. only used check valve in hot out)
Water supply ON..open closest faucet hotside and bleed all air out (might take awhile cause WH needs to fill)
With WH Tank full.......
Turn Propane Switch ON
Listen/check for spark and main flame----might take a few tries to establish propane flow (if more then 3 then WH may 'lock out' and turn on 'Fault Light' (RED Light at on/off panel) To Reset----turn Switch OFF, wait 30 seconds turn back ON
IF that doesn't work......
Then you will need to test for DC at the Brown Wire coming from circuit board going to 'thermal fuse' (device inside clear tubing) to terminal on T-stat
****Have to test when trying to first light off---before it 'locks out'
Is it time for your medication or mine?
2007 DODGE 3500 QC SRW 5.9L CTD In-Bed 'quiet gen'
2007 HitchHiker II 32.5 UKTG 2000W Xantex Inverter
US NAVY------USS Decatur DDG31