I have a 99 gmc yukon my break lights stop working i changed the break switch checked the fuses and bulbs

Do you have power in and out of the brake light switch ?

There is no adjustment. The park lights are on a different circuit than the brake lights.
Do you have a third brake light that works. Its also on a different circuit but works from the same switch. Do your turn signals work. They use the same filament as the brake lights.
Also, the brake light circuit goes through the multi function (turn signal) switch.

Since the brake lights and turn signal lights use the same filament in the bulbs, the brake light circuit will pass through the turn signal switch. When a turn signal is used it cancels out the brake light for that side.

Let me know if your third brake light and turn signals work in the rear.
Also, if youy have not already, check/change the bulbs. The type of sockets those lights are in also get burned so look at them well.

as both stop lights work off the same fuse thats not ur problem check the bulb.

It is probably the stop light switch on the brake peddle but check the stop light fuse first .....

here is a wiring diagram. Are the bulbs for sure good?


hope you can read it.

Change the break light switch under the brake pedal. I have a 97 yukon and it's probably the same, it is really hard to get to. You have to take off the panel under the stirring wheel then look directly behind the brake pedal, it's a big white plastic piece you have to to unplug it. It took us an hour to get it off

is it working? are the brake lights working? is there a blown fuse? why was the switch replaced?

Do your rear turn signals work? If not, I would bet you have a bad turn signal switch.

have you tried replacing the switch on the gearbox????

You probably already know this, however the GMC 2002 Yukon Denali uses the Wagner 3157 (or equivalent) dual element bulb. The running light uses one element whereas the brake & blinker share the other element that burns brighter.

Check to ensure the correct bulbs are being used. Then check all wire harness connections. Since the blinkers function, then it sounds like the connections are good.

It really sounds like there is a bulb issue, so check that first, then let us know the results.