Both left and right brake lights not working, third brake light works

[GREGB1954]

Just as the title states, both the left and right brake lights are out but the 3rd brake like works. I just changed one lamp about 6 months ago and admitedly I have not checked the bulbs other than I did remove and reinsert. Is this a known problem with an obscure solution?

 

[Tonyv__]

Just as the title states, both the left and right brake lights are out but the 3rd brake like works. I just changed one lamp about 6 months ago and admitedly I have not checked the bulbs other than I did remove and reinsert. Is this a known problem with an obscure solution?

I mean you can chase all your grounds and drive yourself crazy or just go the simplistic route and change the bulbs first.

I’ve had bulbs fail shorter than others.

 

[TollKeeper]

This was a fairly common problem on the GMT Vans, which I believe still use the same style of system. The issue for them revolves around a faulty turn signal switch.

If I am remembering correctly, the way to test it is to just turn on your turn signals... If I am remembering correctly, they use the same bulbs as your brake lights. If the lights turn on for turn signal, but not brake, than its the turn signal switch.

 

[Joseph Garcia]

^^^^^x2^^^^^

 

[Doubeleive]

easiest thing to do is a grab a couple bulbs for $3 and swap them out.
THEN, if no go proceed to other possibilities
no reason to presume anything else.....
will take a whole 5 minutes of your day

 

[OR VietVet]

Is there not a separate fuse for the left and right brake lights and the third brake light, also called high mounted brake light? To me, it makes no sense for all bulbs to go bad at same time. Could be the t/s switch but check for separate fuses.

 

[GREGB1954]

Problem solved. I'd like to say that I performed some brilliant episode of deep electronic analysis and replaced a 20' harness that weaved from the engine compartment into the dash, which I had to R&R, through a channel in the body all the way to the rear of the vehicle. But being that I am an honest guy, I replaced 2 defective bulbs for $12 and solved the problem. I was going to do that before I submitted this thread but thought the odds were too remote that both went out when I had just changed one 6 months ago. One key thing to remember though is to NOT touch the bulb glass with your skin. The oils will damage the glass and shorten the life, which is probably what I did.

 

[Fless]

Problem solved. I'd like to say that I performed some brilliant episode of deep electronic analysis and replaced a 20' harness that weaved from the engine compartment into the dash, which I had to R&R, through a channel in the body all the way to the rear of the vehicle. But being that I am an honest guy, I replaced 2 defective bulbs for $12 and solved the problem. I was going to do that before I submitted this thread but thought the odds were too remote that both went out when I had just changed one 6 months ago. One key thing to remember though is to NOT touch the bulb glass with your skin. The oils will damage the glass and shorten the life, which is probably what I did.

Aren't the bulb globes all plastic now?

 

[OR VietVet]

Problem solved. I'd like to say that I performed some brilliant episode of deep electronic analysis and replaced a 20' harness that weaved from the engine compartment into the dash, which I had to R&R, through a channel in the body all the way to the rear of the vehicle. But being that I am an honest guy, I replaced 2 defective bulbs for $12 and solved the problem. I was going to do that before I submitted this thread but thought the odds were too remote that both went out when I had just changed one 6 months ago. One key thing to remember though is to NOT touch the bulb glass with your skin. The oils will damage the glass and shorten the life, which is probably what I did.

Great. Yes, try to not touch any bulb surface.

 

[GREGB1954]

Aren't the bulb globes all plastic now?

Perhaps they are, but there was a very tiny little picture on the packaging indicating that we should not touch the surface.

 

[strutaeng]

Is there not a separate fuse for the left and right brake lights and the third brake light, also called high mounted brake light? To me, it makes no sense for all bulbs to go bad at same time. Could be the t/s switch but check for separate fuses.

Yes, I also had this problem on my K3500 OBS: the taillights didn't work but the cab brake light did. Some random dude mentioned my brake lights didn't work, like months after I bought the truck, LoL

I changed the brake light switch, then the multifunction switch (turn signal lever), and finally found some hacked wiring and missing large fuse on fusebox.

I think what happened is the multi function switch was bad and PO was trying to Jerry rig something.

IIRC the cab brake light doesn't go through taillight circuit. Not sure why it was designed like that, maybe a fail-safe idea? And I didn't (or can't confirm) that it carried over into the later generations

 

[Geotrash]

Problem solved. I'd like to say that I performed some brilliant episode of deep electronic analysis and replaced a 20' harness that weaved from the engine compartment into the dash, which I had to R&R, through a channel in the body all the way to the rear of the vehicle. But being that I am an honest guy, I replaced 2 defective bulbs for $12 and solved the problem. I was going to do that before I submitted this thread but thought the odds were too remote that both went out when I had just changed one 6 months ago. One key thing to remember though is to NOT touch the bulb glass with your skin. The oils will damage the glass and shorten the life, which is probably what I did.

Nice to know I’m not the only one who does stuff like this!