89 200 middle computer reaadout

[TRACY.M.FINNEGAN@monsanto.com]

     hi all,
     a new problem just developed.  when headlights are off, the middle 
     computer readout (bar, mpg, gall, etc) illuminates just fine.  
     however, when headlights are on, this computer loses its backlight, 
     and data is no longer visible in pitch black cockpit.  all other gages 
     and upper computer display (radio station) work fine.  i know how to 
     remove the instrument cluster from past bulb changes.  so, does 
     anybody have a reason why this gage doesn't work with the lights on?
     
     tracy m finnegan
     tmfinn@monsanto.com