parts identification on an old shasta compact.

The fitting on the lower left looks like a hose connection for the pressurized water system.

The fitting on the lower right looks like a water fill to the fresh water tank to be used with a pump.

The fitting on the upper right is the power cord.

The fitting on the upper left is possibly a sink drain, Not really sure though. You should be able to go to the opposite side and see where it goes. It would be the easiest way to tell. JMO