HouseCallAuto 3/18/2010Vehicle Application: 1994 Ford F-150 Super Cab 5.0L, Vin N, Eng Cfg V8 1995 Ford F-150 Super Cab 5.0L, Vin N, Eng Cfg V8
Customer Concern: The speedometer is inoperative. The odometer lights up and shows the mileage. The differential speed sensor has been replaced.
Tests/Procedures: 1. Drive the vehicle while monitoring the odometer operation. If the odometer increases as it should but the speedometer is inoperative, replace the instrument cluster.
2. If the odometer is not increasing along with the speedometer not working, access the 12 terminal connector at the back of the instrument cluster. Check the AC voltage between pin 4 Red/Pink (R/PK) and pin 5 Light Green/Black (LG/BK) from the differential speed sensor. The AC voltage should increase with speed and normally read roughly 1.5-2v AC at 30 MPH and about 3.5-4v at 70 MPH. If the voltage is incorrect, check each wire for high resistance or open circuit between the instrument cluster and differential speed sensor and repair the harness as needed.
3. If the AC voltage is OK, check the powers to the instrument cluster on pin 1 Light Green/Yellow (LG/Y) wire and pin 3 White/Purple (W/P) wire. Also check the ground on pin 2 Pink/Orange (PK/O) wire. If the powers and grounds are also OK, suspect a faulty Programmable Speedometer Odometer Module (PSOM) which is serviced as part of the instrument cluster. Replace the instrument cluster as needed.
Potential Causes: Harness
Hope this helps
Kevin - HouseCall Auto Mechanics