What is an ignition source?

The list of ignition sources listed in the code is “inclusive not exclusive”. Basic rule of thumb is: if it gets hot enough (or could get hot enough) to ignite something, or if it creates a spark, then it is an ignition source.
All switches, motors, lights, exhausts, flues, combustion air intakes, batteries, pumps, motorized jockey wheels, electric gas valves (and more) are ignition sources!
Items required for vehicle safety are exempt. This inludes such iems as electronic stability controls, electric brakes, Anderson plugs, break-away coupling, encapsulated gas safety valves, are exempt. See Clause 3.1.8