Metal Halide Lamp Failed to Strike

Common Symptoms

• Tower mast raises and genset runs normally but one or more lamps stay dark
• Panel LED fault indicator flashes or holds a code 9 after lamp warm-up period
• You can hear the ballast click or buzz but no arc ignites in the lamp
• Lamp flickers briefly at startup then goes out within 30 seconds
• Other lamps on the same tower light normally while the faulted lamp stays dark
• Restarting the unit does not clear the fault and the lamp stays dark
• AC output voltage at the lamp socket is present but lamp does not respond

Probable Causes (Ranked by Likelihood)

• Lamp bulb is at end of life and the arc tube can no longer strike reliably Very Likely
• Lamp socket pins corroded or oxidized, preventing good electrical contact Likely
• Ignitor module worn or failed, not generating the high-voltage pulse needed to start the arc Likely
• Lamp attempted a hot re-strike before the bulb cooled down, causing a normal no-strike condition Possible
• Ballast transformer degraded or failing, not supplying correct open-circuit voltage to the ignitor Possible
• Wiring harness chafed or connector to lamp head loose or burned at the plug Possible
• Wrong replacement lamp installed (incorrect wattage or base type for the ballast) Less Likely

Step-by-Step Diagnostic Procedure

1. Step 1. Let the unit run 5 minutes from a cold start. Metal halide lamps need time to strike. If the lamp still does not light after 5 minutes, the fault is real. A hot re-strike attempt (restarting within 10-15 minutes of shutdown) is normal and not a lamp failure.

2. Step 2. Power the unit down, lower the mast, and allow lamps to cool 15 minutes. Swap the suspect lamp with a known-good lamp from another head on the same tower. Raise the mast and restart. If the fault follows the lamp, the bulb is bad. Replace it with the correct wattage metal halide lamp specified on the ballast label.

3. Step 3. Inspect the lamp socket with a flashlight. Look for green or white corrosion on the socket pins and lamp base contacts. Clean light corrosion with fine-grit emery cloth or electrical contact cleaner. If the socket pins are burned black or melted, the socket needs replacement.

4. Step 4. With the unit running and the lamp circuit energized, use a multimeter set to AC voltage and measure voltage at the lamp socket terminals. You should see 120V AC or 240V AC depending on your model spec. No voltage means a wiring or ballast problem upstream.

5. Step 5. If voltage is present at the socket but the lamp will not strike, the ignitor module is suspect. The ignitor generates a high-voltage pulse (up to 4,000V peak) to start the arc. Testing the ignitor pulse requires a specialty high-voltage probe. If you are at this step, call a qualified tech to bench-test the ignitor.

6. Step 6. Inspect the wiring harness from the ballast box to each lamp head. Look for chafed insulation, pinched wires at the mast hinge points, and burned or melted connectors. Repair any damaged insulation with high-temperature wire sleeve before returning the unit to service.

7. Step 7. If swapping a known-good lamp does not resolve the fault and voltage is confirmed at the socket, the ballast transformer itself may be degraded. Ballast replacement requires panel disassembly. At this point, document the fault code, note which lamp head is affected, and contact a Wacker Neuson service dealer.

Frequently Asked Questions