the incoming signal is 12 volt and the PNP inverter (if that is a correct term) requires a +12 connection. And then the 12 volt was going to be sent out to power the remote gps and compass. What I write shouldn't be worried over. I don't know much, but have mocked all this up and am now building the "final" installation. sometimes I make incorrect assumptions forgetting that if i change two things simultaneously, i won't know which change had the effect I'm now confronted by.
i re-read the max232 data sheet, and as you say, it uses little power.
thank you for thinking about this.
john