The two-speed rear axle air shift system has an electrical circuit that re-calibrates the speedometer to match the selected rear axle ratio. The main components of the system are air pressure-operated and not affected by this circuit. Problems with the electrical circuit will only affect speedometer operation.

The AUX 2 Circuit Breaker supplies battery voltage during RUN or START to the two-speed rear axle air shift switch, terminal A. The air pressure-operated, two-speed rear axle air shift switch is normally closed. With no air pressure available, battery voltage is supplied from the two-speed rear axle air shift switch, terminal B to the Speedo Adapter, terminal A1.

When the two-speed rear axle control valve is placed in the HIGH position (opened), and with sufficient air pressure available in the reservoir, the shift system's air pressure increases to about 35 kPa (5 psi.) The two-speed rear axle air shift switch opens. Battery voltage is no longer present at the Speedo Adapter, terminal A1. The Speedo Adapter then changes calibration so the speedometer reading matches the road-speed for the higher axle ratio selected. As the shift system's air pressure increases, the two-speed rear axle actuator shifts from low-range to high.

When the two-speed rear axle control valve is placed in the LOW position (closed), the shift system's air supply is closed off and residual air pressure is vented to the atmosphere through an exhaust port in the two-speed rear axle quick release valve. There is no pressurized air available at the two-speed rear axle actuator and the two-speed rear axle air shift switch. The two-speed rear axle air shift switch closes and the Speedo Adapter receives battery voltage at terminal A1 from the AUX 2 Circuit Breaker. The Speedo Adapter then changes calibration so the speedometer reading matches the road-speed for the lower axle ratio selected. As the shift system's air pressure decreases, the two-speed rear axle actuator shifts from high-range to low.

When the two-speed rear axle switch is in the LOW range, the Speedo Adapter receives a voltage signal at terminal A1, from the AUX 2 Circuit Breaker through the two-speed rear axle shift relay coil, terminal 86.

When the two-speed rear axle switch is placed in the HIGH range, a ground signal replaces the voltage at terminal A1. This condition changes the electronic calibration of the Speedo Adapter, maintaining an accurate vehicle speed output of the Speedo Adapter when the rear axle shifts to a higher gear ratio.