The quartz speedometer utilizes an accurate clock signal supplied by a quartz crystal, along with integrated electronic circuitry to process an electrical speed signal. This eliminates the need for the conventional speedometer cable. The speed signal is used by the circuitry to drive the core gage and odometer stepper motor. The electrical speed signal is generated by a Permanent Magnet (PM) generator mounted in the transmission. This speed signal is transmitted to the speedometer assembly buffering circuit contained in the instrument cluster circuitry.
You can gain access to the speedometer and tach by removing the front cluster lens, however, knowledge of instrument circuit checks will help in determining if operating difficulties lie in the instrument itself or its related circuit. The speedometer and tach themselves should be serviced by a Specified Service Center. If a speedometer problem develops, it is suggested that you contact an authorized Pontiac dealer.