The fuse for the brake lights in a 2005 GMC Envoy XL is located in the underhood fuse block. To access the fuse block, open the hood of your vehicle and locate the black plastic cover on the driver's side of the engine compartment. Remove the cover by squeezing the tabs on the side and lifting it up.
Once you have removed the cover, you will see a diagram of the fuse block on the inside of the cover. The fuse for the brake lights is labeled "STLP LPS" and is located in the bottom row, second from the right. The fuse is a 15 amp fuse.
If the brake lights are not working, you can check the fuse to see if it is blown. To do this, remove the fuse from the fuse block and inspect the metal strip inside the fuse. If the metal strip is broken, the fuse is blown and needs to be replaced.
To replace the fuse, simply insert a new 15 amp fuse into the fuse block in the same location as the old fuse. Make sure that the new fuse is fully seated in the fuse block before closing the cover.
