Troubleshooting Hints - Exterior Lights

PERFORM BEFORE BEGINNING SYSTEM DIAGNOSIS
1. If only one lamp is inoperative, check the wires to connector for opens (see schematic). Check for an open bulb. Also check for corrosion and/or obvious damage at the connector and terminals.
2. Make sure grounds G115, G116 and G401 are clean and tight.
3. If vehicle is equipped with Daytime Running Lamps (DRL), Refer to "Daytime Running Lamps," for additional exterior lighting diagnosis.
^ Check for a broken (or partially broken) wire inside of the insulation which could cause system malfunction but prove "GOOD" in a continuity/voltage check with a system disconnected. These circuits may be intermittent or resistive when loaded, and if possible, should be checked by monitoring for a voltage drop with the system operational (under load).
^ Check for proper installation of aftermarket electronic equipment which may affect the integrity of other systems (Refer to General Troubleshooting Procedures). Diagnostic Aids
^ Refer to System Diagnosis. System Diagnosis - Exterior Lights