The factory service manuals I have are for my 92. The 92 interior and the 89 are two different animals.
When you say "computer control and the Bose speaker relay" do you mean the control unit and relay for the radio or the cars PCM? I'm guessing the radio control unit.
My 92 has the base Delco radio in it with a head unit and a CDM under the passenger side. It's extremely easy to get to if you enjoy working upside down with your feet in the air and no room to get your hands in to it. I've replaced it twice.
On a 92 you pull the all the parts you can under the dash, the air vent and the glove box. The gives you enough room to almost see it. The rest is accomplished by feel with lots of scraped hands and band aids.
Sorry I can't offer any help on the layout of an 89.
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