Headlight sockets

2009 Chevy Cobalt LT. The driver’s side headlight was out last week, and replacing the bulb didn’t do anything. I spent too long looking for my VOM, and finally pulled the headlight assembly, then pulled off the headlight connector. Inspection showed that the plastic around the center socket looked melted. I decided to just replace the socket. It was on the shelf at Pep Boys and less than $8. When I started the replacement, I noticed there were actually two sockets with pig tails in the package. I decided to put the other one away. You never know when you might need it. Well, this week I did need it. The passenger side headlight went out, and inspection showed the same condition on that socket. The headlight seemed fine last week when I replaced the first one. The time was so short I even remembered where I put the extra socket! BTW, the Dorman package said the sockets are good for both 9004 and 9007 bulbs.

I’m posting to get your opinion on whether this was coincidence. I’m leaning in that direction. I use Sylvania 9007 bulbs, not the OEM 9004 bulbs. Still, the sockets are supposed to handle the 9007s without problem. What’s your opinion about how the sockets got that way? Is it coincidence?

The 9007 and 9004 are wired differently, The high beam and grounds and low beam wires are in different spots.
The bulbs are not interchangeable,
If you’re supposed to be using 9004, but are using 9007
When you have your lights on low beam, you’ll really be using high beam
When you have your lights on high beam, they will be off


When I turn the high beams on, the light gets brighter.

It’s possible that a car wired for 4’s might still produce light output in both hi and low beam switch positions with 7’s installed. As mentioned above in the low-beam mode the 7 will output hi-beam. In the high beam mode both the low and high beam filaments might get lit up, probably in series, depending on how they are wired inside the bulb, so it could appear to be brighter than low beam.

It’s also possible that a car wired for 4’s could still work correctly with 7’s on both low and high beam if the pig-tail wiring instructions say how to do that. Using 7’s may indeed be the cause of the melted connector.

But as the bulbs are not interchangeable, and the car is wired for 4’s, seems like the common sense solution is to install the 4’s and be done with it.

Let’s see?

You find both headlight sockets melted, Pep Boys has replacement sockets on the shelf, and replacing the sockets fixes the problem?

There just might be a problem with the headlight sockets for that vehicle.


Yeah I have the same thing but haven’t replaced them yet. I have the H11 bulbs. My right headlight went out so I replaced both of them thinking the other is not far behind and less hassle to do both at the same time. A week later my right one was out again. I looked at the socket and yeah it showed signs of heat. I just bent the prongs a little for the time being and has been fine. I do intend to replace both at some point. Must be fairly common but haven’t had it before.

Your lights will get brighter on high beam because both filaments are likely on.

That could be, but the sockets are 10 years old. They weren’t badly damaged, but the area surrounding the center socket was smoother and shiny, while the rest of the socket was a matte finish. That’s what I refer to as melted. That’s the ground, btw, as shown in the diagram above from @It_s_Me.

I looked up the correct bulbs on line, and the 9007 is the right bulb. I confused the different types of 9007 bulbs, thinking that the 9004 was OEM, when the 9007 is actually OEM. I’ve replaced the bulbs 3 or 4 times, and always used the Sylvania Silver Star Ultra 9007 as the replacement bulb.

I haven’t looked it up but my suspicion is that the replacement lamps are actually higher power than the OEM lamps. Maybe not by much but the connectors are probably marginal to begin with. Do you use dielectric grease in the socket at each bulb change?

BTW- being compatible with the bulb type (form factor) doesn’t necessarily mean they are designed to handle the most power hungry version of that lamp style. It just means it has the proper connector orientation…

Edit- seeing your latest post, they weren’t as melted as I envisioned. Lots of complaints out there where they are physically deformed quite a bit…

From what I can determine the 9007 in any of its forms, basic, silver star, silver star ultra, all are rated at 65 W power. So the melted connector problem must caused by the materials used for that particular car’s connector. The connectors – to be included in the car’s parts list – must pass a quite an extensive test regime I expect; but apparently that regime didn’t test everything. The effects of current, voltage, humidity, temperature and the like can be tested but it’s more difficult to test the effects of time. If the surface conditions of the connector’s contacts changed, oxidized, corroded, etc, and that increased the resistance of the connection, that could increase the temperature the connector materials are exposed to.

It’s interesting that some makes of cars seem to be significantly more trouble free of electrical problems than other makes. Neither my Ford truck nor my Corolla – excepting the starter motor – has ever had much in the way of electrical trouble. And I’ve owned those vehicles for 45+ and 25+ years. But my VW Rabbit, just in the 10 years I owned it, it had quite a bit of electrical trouble, all of which was due to thermal effects on the materials in the connectors and the relay plates. The Rabbit on the other hand, rust-wise, it held up to the salted Colorado roads much better than the truck. Go figure.