Advice on both low beam headlights not working?

Have a 2006 Hyundai Sonata 3.3 V6. Both low beam headlights do not work. All other lights work.

I checked fuses and relays.

I installed new bulbs.

I tried a new lamp switch.

I checked the front of the female headlight terminals with a multi-meter and get 12.41V from ground and power.

I checked the back (back probing) of the female headlight terminals while connected to the headlamp with the car on and lights on and also got 12V. Turned the lights off and lost voltage.

I checked the low beam bulbs with lights on and car started with multimeter and no reading. (Edit: This actually has a reading of 14v directly at the bulb wires)

Front of female headlight wire coming from engine.

Back of female headlight wire coming from engine.

I noticed they stopped working around the time my alternator went out (covered in oil from valve cover leak). New alternator has been installed.

If you measure 12 volts right at the bulb’s pin for the low beam and the light bulb doesn’t light, either bulb is no good, or you got no ground connection to chassis ground on the ground pin of the bulb.

When you measure 12 volts at the power pin to the bulb, next measure the ground pin of the bulb. If it is 12 volts too, that’s a grounding problem. If you measure 0 volts for the ground pin, remove the power connector to the bulb and measure the bulb element’s resistance between the power pin and the ground pin. It should measure 10 ohms or less. If you really can’t figure it out, remove the bulb entirely and power it up with jumper wires connected to the battery posts. If it doesn’t light that way, you know the bulb is no good.

One caveat: Some high intensity head light bulbs on newer cars require more than 12 volts, and they have special circuity to provide this higher voltage. If you have that type of bulb, forget what I suggested above; instead you’ll need the advice of somebody who has that sort of expertise.

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Bad ground.

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The plug you’re showing isn’t the plug to the bulb itself.

You need to test for power at the plug that goes to the bulb

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Starting to tinker with this issue again. With car started and headlights on, multimeter red probe on + battery and black probe on both bulb wires (black and green) measure at 14.29 Volts. Headlights off, same thing. With car off both bulb wires measure at 13.33 Volts.

So this is a ground issue?

@sonata2006 Frankly I don’t understand why you continue to mess with this vehicle considering the number of problems you seem to have with it.

According to the diagram I’m looking at the headlight bulbs for an 06 Sonata 3.3L have orange and red wire for power, and black for ground. So I’m confused when you say you are measuring a green wire. Double check you are probing the actual headlight bulb pins.

Then do the measurement again, this time measure the voltage between the orange and black, then the red and black, with the headlights on or off and the engine running.

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I only see orange and red wires on the harness going to the headlamp case (which also had voltage). This…

I was testing these two green and black wires directly at the bulb…


It’s hard to tell from here how the red, orange, and black wire at the harness connector get translated inside the headlamp case to the green and black wires. If you can’t figure that out by visual observation, try measuring between the green wire and chassis ground (at the battery negative post), and also the black wire and chassis ground. Same as above in other words, only using the red and black wires inside the case rather than the orange and red wires outside the case. And using the battery negative post for ground. Report your measurements.

Is there just one bulb for both high and low beams? Or are there separate bulbs for high and low? All the cars I’ve dealt with have just one bulb for high and low. But yours may be different, and that may be causing some confusion.

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I’ll try and see how the harness wires configure through the headlamp case. Should be just three screws to remove the whole headlamp case, so I can get better access to the wiring. I got zero on the multimeter when I had the meters black probe on the battery ground and the meters red probe on both green and black wire on the bulb (with car on and lights on) is that what you mean by measurements between green and ground (battery post)?

There are two bulbs. One for hi and one for lo. Also fog lights.


Do you get the same voltage readings (above) with the headlight switch OFF?

Yes, 14v at wires at bulb with car on and lights on and off.

To me, this says bad switch, bad fuse, or break in power wire to low beams.

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I tried a new switch and no go, maybe something in the connector that switch connects to? I checked and even replaced fuses. Swapped hi and lo relays. If there was a break in power wire to low beams wouldn’t that mean two breaks in the same wire because there are two harnesses for the headlamps? If it was ground wouldn’t other items not work that share the same ground?


If it is a grounding issue. Would it be Ground 20 from this diagram? It looks like ground 20 is shared with left front fog lamp (which works)

Headlight diagram

Fog light diagram

Anyone know where ground 20 is located from this image? Is this inside the car?

It also seems there is a low headlight relay under the shift lever console???

That is an unusual test method but using the headlight connector as a ground and being able to measure the battery voltage proves that the headlight has a ground, to be clear, there is no power to the headlight.

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Fuses are checked by verifying power into and out of the fuse, knowing if there is power to the fuse is important diagnostic information.

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Sorry, I do not follow. Use the black multimeter lead on the black wire terminal of the headlight connector and connect the red lead on the multimeter to the battery positive?

I had voltage (believe 12.44 with car and lights off) on the inside of the relays and fuse locations.

That is what you stated you did and read 14.29 volts.

Normally the ground lead is connected to the negative battery post and the red lead is used to measure voltage at the test points but we know now that there is no power at the headlight connector.

The schematic shows that fuse 10 has power with the ignition “on”, did you check fuse 10 in the junction block?

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