There is a "box" under the front passenger seat. It looks like an early amp or something, could be aftermarket, but I doubt it. The car had no radio when I got it, so I have no idea what it had for a radio stock. If anyone else had this, please let me know its function and application. Thanks,

There is nothing located under the passenger seat from the factory in the digital dash ('84 - '86) Berlinettas. The stock radio was mounted on a pedistal on the console behind the ash tray and the radio swiveled left & right. There was also a second radio module located under the console panel behind the pedistal radio. The pedistal radio plugged into the radio module & the radio module had the standard GM radio sockets for speakers, power, antenna, etc. The pedistal radio was available with a casette player, or a filler panel in place of the casette deck. Both models had a digitally controlled 5 band EQ, fader, balance, and volume controls & was designed to drive four 16 ohm speakers. If you plan on using an aftermarket radio in its place, you will need to fabricate a block off plate for the hole where the pedistal mount radio used to be, and cut a rectangular hole in the near vertical portion of the console for the new radio. The A/C ducting behind where the hole is cut will most likely need to be modified to accept a standard depth head unit, unless you don't mind having a portion of the head unit protrude past the console panel - it won't mount flush with the console panel because it will hit the unmodified A/C ducting.

If you bypass the swivel mount radio wiring harness, you can mount a new head unit under the pass side dash. That swivel mount is just too damn cool to remove. If you do this though, you have to connect the wiring harness from the new radio onto the input of the box inside the center console, which is the actual radio module.

Just realized how crappy my explanation looks next to Tims.

Like I said, it had no radio when I got it. That also entails no center console cover, where the power windows, shifter, and all other manners of things mount up. I had no parts of the sock radio left, minus the place where it would mount up. I put in a cd player over a year ago, and had a plastic housing made to fill the gap where the stock radio would go. I still have no idea what that box is though...

Its a gray metal box undereath where the stock radio would have gone. Post a pic of what you found under your seat, maybe it just got stuffed there. If youre really into getting a stock radio, check the yards, or ebay. Ive got an extra one, but its buried somewhere in my parents house, otherwise id let it go for cheap.