For the water heater, the outside switch, with the little hair pin, is electric only. The inside switch, is for propane only. You can run both at the same time. As for the inside switch, move it one direction, and stand back and wait. Wait some more, and watch for the light. The light will only come on while trying to light. If all is successful, it will go back out. The sequence may take 3o seconds or longer. If the light stays on, you have a failure to light, and will have to troubleshoot that. It will not happen the moment you press the switch, you must wait. Most of the switches I see now days, the factory has in upside down, down is on, up is off. Try it both ways.
For a guarantee failure, try to light it with the propane bottles turned off. After a few minutes the light should be steady glow, indicating failure. That will be the "on" position for propane.
2012 Ford F250 ext. Cab 4x4
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2008 Work and Play 18LT