It is a problem, your headlight should never dim when other instruments come on. That's why there is a voltage regulator and relays. Everything is drawn off the Battery, when the battery drops to its minimum voltage the regulator senses that low voltage and the relay closes to charge the battery from the alternator when it reaches maximum voltage (storage) the relay/voltage regulator opens and the charging stops. If you have a bad cell in the battery (it could be shorted or open, just putting a voltmeter on the battery will NOT tell you it has a bad cell, as mentioned it needs to load tested) so the regulator/alternator is always sensing low voltage and the alternator is continuously charging so when you hit your brake or any high currnet draw device i.e lights it is drawing off the alternator which is why it dims because the alternatror (Generator) is a motor andyour revs are reduced slightly when a load is put on the motor/Alternator.

 

Mine does the exact thing. Thought I was going crazy but it's been doing it since the day I bought it 3 months ago. I only have 3500 miles on it, I do drive with the fog lights on and since I live in Phoenix the AC has been on until about a month ago. I thought it was just because I had everything on.

Please let us know what the dealer says. I haven't taken mine in for anything yet. I have a couple of warranty claims, but nothing major. But I will mention this to them as well. They'll probably think I'm nutz.

Thanks
pgaduane

 

mine only has 900 miles on it and does the same thing..Let me know what happens

 

I took it to the chevrolet dealership and they couldnt troubleshoot because they said they arent qualified on hummers but I drove home to Iowa from New Mexico for the holidays so I am going to take it to the hummer dealer up here to see what the deal is.

 

Mine has done this since I got it and I have 47k miles on it and have had it for 2 years. I doubt it's a problem. As the other guys said, it's probably because you drive with your fog lights on or some other accessories, like your AC, Heat/Blower, etc. I wouldn't worry about it. Alot of cars do that believe it or not.

 

I dunno about y'all but I wouldn't accept that as proper mechanical functioning. The electrical system was made to accomodate the load of all accessories on the vehicle from the factory, including fog lights and fan motor. When the battery voltage drops too low and the lights dim then the alternator/generator is working it's rear end off to keep the battery at 14 volts. The battery is SUPPOSED to have enough reserve capacity to be able to run the lights and radio without having a hernia whenever the brake lights come on. I don't expect my old 79 Jeep CJ5 to do that with it's ancient technology and I dang sure don't expect my 07 HUMMER to do it with it's modern electronics either. Lights dimming? There's a problem, it might not be a big problem but it's one that would bug me and it's one the dealer needs to fix.

 

Honestly....Every GM I have ever owned has done that. I wouldn't be too concerned! If it get worse take it in for service....

 

It is a problem, I have had GM's, Ford's, Dodge's, Honda's, VW's, AMC's, Lincoln's, Buick's, Datsun's, GMC's, Scion's, Fiat's, BMW's, Mazda's and none of the many vehicles did my headlights dim unless there WAS A PROBLEM!!!.The Electrical system as I so explained in the previous thread is how it works. IF there is an Certified Mechanic amongst this forum "Please tell me I am wrong".It might seem insignificant to some of you but if you notice it then it has a problem. I would even see if a friends vehicle does it if it doesn't do it "DUH".

 

The wife ownes a '04 GMC Envoy and the thing has had this same issue since the day we drove it off the lot. According to the dealership they have said it is a known issue and GM has no fix for the dimming headlights/instrument panel. Like it was stated before, the dimming happens for a split second especially coming to a stop light and it does not happen all the time. Hope my alpha does not have this issue!!!

 

Gotta agree with Gunny! I'm not a certified wrench but I've turned more than my share of them for many years. If my electrical system was doing that I'd be finding out why because it's NOT right. That's like saying, "Well, GM says it's supposed to stall at every third stop light and it's OK". Bill Gates might be able to get away with a lame excuse like that but Gunny and I and many others here know better. Ifit ain't right, fix it. And a dimming electrical system says, 1) Bad Battery 2) Bad charging system 3) Ground fault short somewhere 4) Bad or crossed connection 5) Some computer glitch that need attention.