W100 1/2 Ton Pickup 4WD V8-360 5.9L VIN 1 4-bbl (1988)
Fig. 9 Speed Control Continuity Chart. 1991 Models
1. Disconnect the blade type four wire electrical connector from base of steering column.
2. Using a continuity tester, or an ohmmeter, check for continuity at connector wires. Do not use a test light.
3. Results should be obtained according to the charts. If these results are not obtained, replace switch.