280Z- Solid blue is power, solid black is ground. Three prong connector is power antenna (Blue/Red, blue/white/soild blue) You can piggy back your memory wire to your fuse box wire. Third up from the bottom (door side) This will get your unit to work
A/M wire colors are usually... red=power, black=ground, blue=power antenna, yellow=memory. Speakers are gray, lavender, etc...
When I purchased my 280Z I had the same problem- Stolen radio
If you need further assistance you can email me and I'll give you my number to walk you through it all. I just removed a unit similar to yours from my 280Z to install it into the Z32. LOL.. which is alot easier then installation of both 76 280Z and 83ZXT
Donna