Pickup & 4Runner - Carbureted

Jack up and support one rear wheel off ground. Release parking brake. Place shift lever in Neutral. On 4WD models, ensure transfer case lever is in "2H" position.
Unplug wiring connector from computer. Computer is located at left kick panel. Using ohmmeter, test "ON-OFF" cycles of speed sensor. See Fig 1. Insert a 10-ohm resistor in series with positive ohmmeter lead. Insert lead in rear of connector. Ground ohmmeter negative terminal.
Slowly turn wheel. Check to see that ohmmeter needle deflects consistently. If ohmmeter needle does not deflect, check that sensor leads are firmly connected to rear of speedometer. If connections are okay, replace speedometer assembly.

Fig 1: Testing Speed Sensor (Pickup & 4Runner - Carbureted)