Programmable Speedometer/Odometer Module (PSOM)
WARNING: This page is about a different car, the 1995 Lincoln Mark VIII. However, it is still accessible from the selected car via links, so may be relevant.
PSOM receives input from Rear Anti-Lock Brake Sensor (RABS). The RABS is mounted to rear axle differential. The PSOM signal is used by speed control module and the PCM.