1990 GMC SLE. When i bought the truck it had a aftermarket radio in the hole where the tape player/equalizer was. The guy kept the aftermarket radio and I went to a junkyard and purchased the original like tape player/equalizer. It lights up but when I press the equalizer buttons I just get the centre line to light up on that button and nothing happens. Is the equalizer junk or is it in the wiring. I believe I just plugged it into the radio with a sealed plug.