Left side low beam out

Welcome to 2CarPros.

If you are getting 12v to the light socket, the bulb is good, and there are no connection issues with the plug, then it has to be a ground related problem. Since you have power, a fuse is unlikely, but each beam and side has its own fuse. See picture 1.

Next, I need you to check for a good ground to the left light. See pic 2 for location.

Here are a few links you may find helpful:

https://www.2carpros.com/articles/how-to-check-an-electrical-relay-and-wiring-control-circuit

https://www.2carpros.com/articles/how-a-car-fuse-works

https://www.2carpros.com/articles/how-to-check-a-car-fuse

https://www.2carpros.com/articles/how-to-use-a-test-light-circuit-tester

https://www.2carpros.com/articles/how-to-use-a-voltmeter

https://www.2carpros.com/articles/how-to-check-wiring

Let me know what you find or if you have other questions.

Take care,
Joe

Thanks for the quick response, Joe! I’m measuring 12v between the hot and ground wires, not the hot wire and the chassis, so is it still likely to be a bad ground, given that the expected potential difference exists across the wires? If the ground was open, wouldn’t that voltage difference be zero?
In terms of checking the ground, what do you recommend? Thanks again!

Welcome back:

What you said makes perfect sense. However, I've see grounds fail when a load was placed on it. Are you certain the socket is good and the bulb is correct? Sorry to ask, but you would be amazed how easy it is today to get the wrong bulb.

Joe

Hi Joe,
I’m pretty close to certain that the socket is good, I just replaced it. The bulb matches the designator on the socket and supply voltage, and worked for about a month after I replaced it (old one burnt out) before it suddenly stopped. When I swapped the bulbs out, I noticed the socket was pretty well melted, although it still worked. Either it was really cheap, or things were getting unnecessarily hot in there. As such, I don’t think it’s the socket or the bulb, but something in the wiring (or connections). Is the headlight ground the one in the engine compartment? There’s also a thick bundle of ground wires that goes deep behind the fender, and I can’t see which is which, since everything’s well wrapped in electrical tape. maybe it’s time I bit the bullet and just unwrapped it all. Is there a non visual ground test you know of?
Thanks,
Ben

Welcome back:

Ben, the easiest thing to do to determine if it is a ground issue is make a new ground. Simply take a wire and attach one side to the light socket ground and the other to the battery ground.

As far as the heat issue with the old socket, that isn't uncommon. I will tell you also that if a connection isn't good and any arcing is happening, that creates a lot of heat.

Try making a temporary ground to see if that resolves the issue.

Let me know.

Joe

Hi there Joe,

I tried connecting to a new ground by tightening a wire under the ground bolt, and the system still did not work. I assume this means it’s not the ground. Any next ideas?
Thanks,
Ben

Welcome back, Ben:

If you are certain that you had a good ground and there is power to the bulb, nothing makes sense. It should light. I need you to check two more things. First, confirm continuity to ground with the new wire. Next, I want you to get a helper and do the following. With the light bulb removed, have the helper turn the lights on. Do you see 12v? If so, keep the multi meter attached to the power wire and plug in the bulb. Do you still have 12v?

If you have 12 volts constant and a good ground, something in the bulb isn't making contact because the power has no choice but to follow the circuit to ground.

Electricity is nothing more than the continuous flow of electrons through a conductor. In this case, you have a wire where the power comes from (that has power), a bulb in the middle (that power should travel through) that should light when power is applied, and in the end, a ground that completes the circuit. Electricity always finds the easiest way out, so a ground is easiest. With all of that, if power is present, the bulb is good and connected, and the ground is good, there is nothing else to do. It should work.

The only thing I question, and I asked you to check, is if a switch is bad, a ground is weak, or the wire has a partial break in it, when the light bulb draws power, the circuit may fail. That is why I need you to check if the voltage drops from the supply when the bulb is installed.

Sorry for electrical lesson. LOL Sometimes it's easier to picture it in your mind and I tried to paint that picture. With that, either I confused you or helped you. I'm hoping for helped.

Let me know what happens.

Take care,
Joe

Hi Joe,
I’ll run that test as soon as I get a chance.
I’m wondering if it might be a loose connection or broken wire on the hot side, or under the fuse box. To test the bulb and socket once and for all, though, and make sure that combo works, could I connect the hot and neutral wires directly to the battery?
Thanks, Ben.

Welcome back:

Try using the wiring straight from the supply. Otherwise, if there is a problem, it may not fail.

Let me know what you find, Ben.

Take care,
Joe

Would you consider it imperative to include a fuse on the wire between the hot terminal and the bulb if I’m not cranking the car while I do the test? Also, is there a protective mechanism in the battery that requires a certain load to supply current, for short protection?
Thanks,
Ben

Welcome back:

Ben, since you are just testing for a very brief amount of time, I don't see a need for it to be fused. However, I like how you think. I wish more people were as conscientious. As far as a minimum load, nothing like that. When you hook to the battery, it's direct.

Be careful and let me know if you have questions or if I can help.

Take care,
Joe

Thanks, Joe.

I took the socket and bulb out of the headlight housing, and set one wire directly on the positive post of the battery and one on the ground. While there was a limited amount of contact since I was only holding the wires there, I didn’t get so much as a flicker from the bulb. Do you think this means that the bulb/socket combo is bad, or should I attach the wires more firmly to get a conclusive result?
Thanks, Ben

Ben:

Do you have a multi meter that you can use to check for continuity? If you do, plug the bulb into the socket and check if there is continuity between the two wires. Basically, you are checking to see if power will go in one end and out the other (go through the bulb). I will say that if you had ground and put power directly to the socket, it should have lit.

Let me know if you can.

Joe

Hi Joe,
Apologies for the delay in responding. You might’ve hit the nail on the head. I’m not getting continuity when I connect the leads to the socket wires with the bulb plugged in. However, doesn’t it also make sense that there simply may not be enough current passing through the filament, given what must no doubt be its high resistance?
Thanks, Ben

Welcome back, Ben.

No, either the bulb is bad or where it connects in the socket is not touching or the socket is just bad. Remove the bulb and place your multi meter on the two connections for the bulb and see if there is continuity. That way we can confirm if it's the bulb or the socket.

When you check for continuity, you are basically sending a small amount of voltage through the circuit. You are correct in thinking the bulb needs more power to light, but power will still pass through if there is a complete circuit (aka continuity).

Let me know what you find.

Joe

Hi there Joe,
We have a winner! Socket was the culprit. Swapped that out and everything works great now, so it must have been faulty from the factory. Thank you for all your help, you saved me hundreds of dollars, and have helped build my confidence in fixing my car. All the best!
Ben

Welcome back:

You are very welcome, Ben. I could tell you were the type of person that would figure it out. Anytime you need help, you are always welcome back here. Trust me, you can do a lot more on the car than you think. We all have to be shown how the first time.


Take care and hope to see you again if you need something

Joe