Commercial/Shore Power Connection

[Crabber82]

Thank you Charlie...That's exactly what I was trying to avoid. Expensive first timer mistakes....

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Hi Mike, The 30a cord had one of those on it when I took it out of the storage been. However, when I plugged it in and switched the power selection to 30A I didn't seem to have any power in the living area. When the onboard generator is running (no commercial power connected) all the features on the bus function as I would expect.
I am fairly certain that the house batteries (not engine or generator battery) are dead. Would this be the reason that the house lights are not performing on commercial power?
I would have thought that when plugged in that the commercial power would be the source. But I am beginning to think that this is not the case...Any words of wisdom for the "newbie".

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On a follow up note in the quest to further my power station knowledge. There are three ports in the power station compartment. The owners manual (yes I have the original one from 1988) does not really explain what is going on in this area. So would someone shed some light on the correct usage of these ports.
Top left port appears to be 50A service, top right appears to be another 50A service and bottom right appears to be the 30A service.

Guessing it is fairly safe to assume...never use two of these at same time?