Four Wheel Drive Indicator Lamp: Testing and Inspection

On each of the lamps found depends upon a hard wired circuit input to the instrument cluster for proper operation. The following procedures will help to diagnose conditions that may cause an inoperative hard wired lamp circuit condition.

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Four-Wheel Drive Lock Indicator Lamp
The diagnosis found here addresses an inoperative four-wheel drive indicator lamp condition. If the problem being diagnosed is related to lamp accuracy, be certain to confirm that the problem is with the lamp or switch and not with a damaged or inoperative transfer case or transfer case linkage. Refer to NV231 Diagnosis or NV242 Diagnosis. If no transfer case problem is found, the following procedure will help locate a short or open in the indicator lamp circuit.
1. Check the fused ignition switch output (run/ start) fuse in the junction block. If OK, go to Step 2. If not OK, repair the shorted circuit or component as required and replace the faulty fuse.
2. Turn the ignition switch to the ON position. Check for battery voltage at the fused ignition switch output (run/start) fuse in the junction block. If OK, go to Step 3. If not OK, repair the open fused ignition switch output (run/start) circuit to the ignition switch as required.
3. Turn the ignition switch to the OFF position. Disconnect and isolate the battery negative table. Disconnect the transfer case switch wire harness connector. Check for continuity between the ground circuit cavity of the transfer case switch wire harness connector and a good ground. There should be continuity. If OK, go to Step 4. If not OK, repair the open ground circuit to ground as required.
4. Connect the battery negative cable. Turn the ignition switch to the ON position. Install a jumper wire between the four wheel drive lock indicator lamp driver circuit cavity of the transfer case switch wire harness connector and a good ground. The four-wheel drive lock indicator lamp should light. If OK, replace the faulty transfer case switch. If not OK, go to Step 5.
5. Turn the ignition switch to the OFF position. Disconnect and isolate the battery negative cable. Disconnect the wire harness connector at the Controller Anti-Lock Brake (CAB). Remove the instrument cluster. With the transfer case switch wire harness connector still disconnected, check for continuity between the four wheel drive lock indicator lamp driver circuit cavity of the instrument cluster wire harness connector B and a good ground. There should be no continuity. If OK, go to Step 6. If not OK, repair the shorted four wheel drive lock indicator lamp driver circuit as required.
6. Check for continuity between the four wheel drive lock indicator lamp driver circuit cavities of the instrument cluster wire harness connector B and the transfer case switch wire harness connector. There should be continuity. If OK, replace the faulty bulb. If not OK, repair the open four wheel drive lock indicator lamp driver circuit as required.