Third BRAKE light stopped working

jhilario72 · Dec 18, 2023

On my 2003 Denali XL, I noticed that the third break light stopped illuminating when breaks are applied. The normal break lights go on. Is there a fuse or something that controls the third break light? Or is it a single bulb that burned out?

Thanks!

gooffeyguy · Dec 18, 2023

Probably burnt out. The one on my 2001 has before and the entire red plastic lens/housing gets replaced and just plugs in back behind it

OR VietVet · Dec 18, 2023

No separate fuse. Replace the whole thing. Easy to get to and check power and ground.

Fless · Dec 18, 2023

Contrary to what you've heard, there's a fuse for it in the in-cab lefthand fusebox (VEH CHMSL):

OR VietVet · Dec 18, 2023

Fless said:
Contrary to what you've heard, there's a fuse for it in the in-cab lefthand fusebox (VEH CHMSL):

View attachment 416822

That's not for the 3rd brake light. That is for "Chair Heat Module Seat or Leg". :chewie:

Everyone knows that!!!!!

OR VietVet · Dec 18, 2023

If the CHMSL stands for "Chassis mount stop light". Aren't they all chassis mount? Please break down the CHMSL, thanks.

Fless · Dec 18, 2023

OR VietVet said:
If the CHMSL stands for "Chassis mount stop light". Aren't they all chassis mount? Please break down the CHMSL, thanks.

Center High-Mounted Stoplamp

OR VietVet · Dec 18, 2023

Fless said:
Center High-Mounted Stoplamp

View attachment 416836

Ok, ok, ya got me. I effffed up. I am going to my room now.....

ScottyBoy · Dec 18, 2023

When my 3rd brake light went out, I unhooked it and checked the voltage at the plug while I had a helper press the brakes. I did indeed have voltage, so I just ordered a new 3rd brake light from Amazon. I don't believe they have a replaceable bulb, I think you do indeed HAVE to replace the entire housing. It was only about $20-$25 it wasn't expensive at all.

mwilson62000 · Dec 18, 2023

Does your cruise control still work? If I remember correctly, years ago in my Tahoe, the CHMSL stopped working and I happened to notice my cruise wasn’t working either. Was the brake light switch under the dash.

Third BRAKE light stopped working

jhilario72

Member

gooffeyguy

Tom

OR VietVet

Multnomah Falls

Fless

OR VietVet

Multnomah Falls

OR VietVet

Multnomah Falls

Fless

OR VietVet

Multnomah Falls

ScottyBoy

Full Access Member

mwilson62000

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