The master switch is a simple DPST switch. There is no difference between the two sets of contacts. My guess is someone switched the contacts on yours when the load carrying set started to fail. Now they are failing to carry the generator field current. Ordinarily, the generator set should long outlast the load set.
The Alpha STC is a good solution, but the mechanical switch lets you go even if the battery is dead. It'll hold up well as long as you don't switch it while it's carrying a load, especially, never switch it while the starter is engaged! John
