As far as powering the screen and switching on/off, I see no need for anything else. And then video input. Is it VGA and RCA? or just RCA? Maybe a URL link to the product would help.
sound of it it's just a RCA monitor. Why would it need audio? Does it function as a tuner/head unit as well. If it doesn't then I don't see why it would need to have audio plugs. I'm thinking, if it has no audio plugs, it is only a monitor. Only video, but again, I can't go look for myself, google didn't provide any obvious products that match your description.
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