When low beam headlights don’t work the problem can be as simple as a blown fuse or as complicated as a bad body control module. I’ll walk you through the diagnostic steps to find out why your low beam headlights don’t work.
Check for power at the low beam headlights connectors
The low beam headlight connector is always the starting point for diagnosing headlight issues. Disconnect the electrical connector from the low beam headlight bulb. Then examine the condition of the connector. Look for melted plastic, corroded pins, or any sign of overheating.
If you find any indication of overheating, STOP and skip down to the testing portion of this article.
Test for battery power
If your vehicle has only one headlight bulb on each side of the vehicle, the bulb contains two filaments, one for the high beams and one for the low beams. The electrical connector will have three terminals: battery power for the low beam and high beam and a ground. With the headlight switch in the ON position for low beams, use a digital voltmeter to test for battery power. Connect the negative meter lead to the battery negative terminal or a good ground spot. Then use the positive meter probe to check for power in each of the terminals of the headlight connector. If you see full battery voltage of 12.2-volts or more on the low beam terminal, power is getting to the low beam headlight. Leave the positive meter lead attached to that terminal and move the negative lead to the ground terminal in the connector. You should read the same voltage. If you don’t get full battery voltage, you have an open in the ground connection. If you get a voltage reading but it’s not the same as when the negative meter lead was connected to the battery, then you have high resistance in the ground circuit. Follow the ground wire to it’s termination point and clean the ground connection and retest.
If power isn’t getting to the low beam headlight
Some vehicles have a separate fuse for the left and right low beam headlights. Refer to the fuse box diagrams in your owner’s manual and check the fuses. If they’re good, check to see if your vehicle uses low beam headlight relays. If so, swap the headlight relay with another relay in the fuse box with the same number. If that still doesn’t work, you’ll have to get a wiring diagram for your vehicle and find out which device switches power to the low beam headlight relay.
In older vehicles, it’s usually the headlight switch. But in newer vehicles, it can be the generic electronic module (Ford), Body control module, Intelligent power module, front control module, etc.
If the low beam headlight connector is melted
Replace with a ceramic pigtail
©, 2016 Rick MuscoplatPosted on by Rick Muscoplat