Is your trailer new? It is quite possible, if it is, that the dealer loaded some water into the tank to test the pump and plumbing joints prior to your picking it up... As a "rule of thumb", the fresh water tank level indicators are the only ones that
won't give you trouble with false readings
You don't mention what trailer you have... Aux could be almost anything. Is it located next to a switch for something? No way of telling without more information. The usual indicators are for Black Tank, Gray Tank, Fresh Water Tank, and Battery. I've seen high end rigs with indicators for LP...but, I don't know if CruiserRV is using that type of system on any of their rigs...? But, an "AUX" indicator light could be anything from the afore mentioned LP system, tank heaters being on, to "scare lights" being on, etcetera, etcetera. Time to get out the manuals or call your dealer
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