Sorry, I thought it was a newer cavalier. The one your mom has can be very tricky because it can indeed be the instrument cluster being the issue. You could try to use my resistor trick but you might have to use a relay being triggered off of the starter wire to send both the proper r value and a ground to the bulb check wire.
try to get on to this website. Not sure if it'll let you or not.
http://www.directeddealers.com/manua...tion_Guide.pdf