brake lights not coming on—new bulbs and fuse

[jimmywalters]

Hey there: I have a 2004 Pontiac Montana, just normal base version. It has three brake lights: two in the actual tail light housing, and one up on top of the rear hatch.
Not sure if both tail light brake lights blew at the same time or separately, but as of right now, neither tail light brake light is lighting up, but the one on top of the rear hatch is lighting up.
Put in brand-new bulbs in both tail light housings, and put in a brand new fuse in the fuse box, but still, neither brake light in the tail light housings is lighting up (although the top one is still fine).
I only know where one fuse box in my car is, and it's mounted right in the side of the dashboard as you open the passenger side door. I replaced the fuse called "stop lamp".

All other lights in both housings appear to work. So now I'm very stuck. If not the fuse and not the bulbs.... what could it be?
Thank you everyone!!

 

[melsg5]

use a voltmeter or test light to determine if you have power going to the bulb sockets.
the other fuse box is under the hood, see fuse boxes starting on page 5-107

http://www.vadengmpp.com/owners-manual/pontiac/2004-Pontiac-Montana.pdf

 

[CDN MONTANA 2009]

Could this be BCM? We have the same problem in 2009 Montana. Different BCM, but same problem. Added some times the other electrics fail. Only when cabin hot due to water or hot weather. Not when cold. Vehicle cools down: problem stops.