Sorry no one has replied to your questions. I'm not familiar with the OEM unit in your car, but it's probably a Hirschmannn? If so, do a search and there is lots of info on removal, replacement, and renewing these fine old units right here in this forum.
If you can get it to power up, then it's worth restoring.

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1986 560SL
2002 Toyota Camry
1993 Lexus