Both Headlights Blow Out at the Same Time
Headlights
are a basic electrical bulb that depends on a constant voltage supply to operate.
If both headlight bulbs go out at the same time the system voltage supplied to the
vehicle is too high. The car's electrical supply level is controlled by the
alternator and voltage regulator.
To test for this condition follow the procedure below: (Always wear protective safety
goggles and gloves before work begins)
Alternator Test Troubleshooting Using a voltage meter connect the meter leads (red to positive and black to the negative terminal of the battery). Then start the engine and allow to idle (do not drive) the voltage should be between 13.6 to 14.3 volts. Now have a helper increase the engine RPM's. The voltage should not go higher than 14.3 volts, if the voltage continues to rise beyond the max limit the voltage regulator has failed and needs to be replaced to prevent further bulb damage. Most alternator systems are designed with internal voltage regulator that cannot be replaced unless the alternator is disassembled. In this case it is best to replace the alternator. After the alternator or voltage regulator replacement is complete replace the headlight bulb and any other bulb effected by the malfunction and recheck system.
If further technical assistance is needed, our certified car repair technicians are ready to answer your car questions. Related Car Repair Information
Alternator Test Troubleshooting Using a voltage meter connect the meter leads (red to positive and black to the negative terminal of the battery). Then start the engine and allow to idle (do not drive) the voltage should be between 13.6 to 14.3 volts. Now have a helper increase the engine RPM's. The voltage should not go higher than 14.3 volts, if the voltage continues to rise beyond the max limit the voltage regulator has failed and needs to be replaced to prevent further bulb damage. Most alternator systems are designed with internal voltage regulator that cannot be replaced unless the alternator is disassembled. In this case it is best to replace the alternator. After the alternator or voltage regulator replacement is complete replace the headlight bulb and any other bulb effected by the malfunction and recheck system.
If further technical assistance is needed, our certified car repair technicians are ready to answer your car questions. Related Car Repair Information