If the speedometer is working then your problem may be an unplugged odometer. (Maybe a previous owner didn't want to stack up the miles?)
Look on the circuit card that the speedometer mounts to. There are two connectors, one for the odometer and one for the trip odometer. Make sure both of them are plugged in. If they are, and the tripodometer is working, you may be able to swap the plugs. If the odometer starts working, then there is a problem on that circuit card. If it's still dead, then the stepper motor that drives the number wheels may be bad. Hope this helps.
Rod Schneider, Woodstock, Ga.
White 88 GT