Brake lights work as long as head/tail lights are off

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  #1  
Old 09-28-17, 11:55 AM
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Brake lights work as long as head/tail lights are off

2000 Chevy Express Van
If I step on the brake all is well unless the head lights are on.
If the head lights are on, the two bottom tail lights go off.
Any ideas? I'm about to google.
 
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Old 09-28-17, 12:02 PM
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It sounds like it could be a ground issue, so I would start by removing the affected tail light bulbs and checking for continuity on the ground side of the socket back to the frame. If that doesn't indicate a problem, as long as I was in there anyway I would then check to see what voltage is going to the positive side of the socket when the headlights are turned on.
 
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Old 09-28-17, 12:09 PM
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Brake lights don't work when headlights are on! - Ask the GM Technician - GM-Trucks.com


Pedro, I found that which coincides with some of what you said. bbiab
 
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Old 09-28-17, 12:45 PM
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As the link said a bad bulb. A filament sags on to another. Been there, been puzzled by that, should have tried new bulbs first but fiddled around looking for a wire problem. Can't say it will work but new bulbs won't hurt and a quick elimination of a possible cause. Assumes traditional incandescent bulbs, does not apply to LED..
 
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Old 09-28-17, 01:13 PM
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It's been a while I guess since I ran into one, so didn't think about it without having it in front of me, but yes, definitely check the bulbs themselves. As mentioned, not the case with some of the newer bulbs, and bulbs in general have come quite a way, but used to be very common to encounter a broken filament.
 
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Old 09-28-17, 02:33 PM
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I replaced all 4 bulbs, each of them has 2 filaments. It fixed the passenger side. After playing with the sockets, the driver's side started to work & the passenger didn't. Did I fix one ground & ruin the other?
 
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Old 09-28-17, 02:54 PM
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FWIW, when I had a bulb fail and the broken filament fall onto the one still intact, the fuse blew. 93 Cutlass Ciera.
 
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Old 09-28-17, 03:12 PM
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I don't think that there is a blown fuse but I have nothing against looking.
 
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Old 09-29-17, 10:26 AM
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It doesn't sound like it to me, either, so I just wanted to point out I had a different result from having what was suggested as the cause of your problem.
 
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