You didn't say if you had pulled the light fixture to check the wiring - sounds like you have a partial short that is drawing right at the circuit breaker rating.
I had the step cover fail on my 2002 Horizon 32td, turned out to be the switch. Carefully pry the switch out of the panel and use a jumper to by-pass it to see if the step works. I got a switch from DigiKey, but Lichtsinn RV also had it. The pneumatic actuator on my Horizon was located on the drivers side under the "hood". That actuator has a couple of manual operation buttons on it that allow verification of pneumatic operation. Those buttons should help determine if the pneumatic cylinder is the problem.
The fuel gauge could be "interesting". I think I have seen some troubleshooting tips for fuel gauges on a forum, either here or on iRV2. Keep in mind the dash indicators/gauges are controlled by the VDU (Vehicle Data Unit) that is mounted in the engine area - look for the 1/4" green & red air lines going to it.
2011 Itasca Meridian 34Y
2006 Jeep Liberty