Make sure you hooked up the remote wire. The premium sound system has a built in amplifier....this is normally (at least on my 91 and 93) located behind the plastic trim on the passenger side behind the rear seats. When I first wired my stereo in, I took the connections out of the amp and ran wires from cork to cork, skipping the amp altogether. If you want to go ahead and use it (I would ditch it altogether honestly), the power and remote wires are up under the dash, on the left side of the transmission tunnel. It will be a yellow wire (power) and a blue wire (remote) in one cork that run back under the carpet toward the amp and also up toward the stereo.
But again, honestly, I would skip the factory amp...with the 91 I just got, I took the whole wiring harness out and ran 16g wire from the head unit to each speaker...
