Why won't the brake lights work

Notice the diagram. Does the high mount stop lamp work? you can see the fuse in diagram, supplies voltage to stop switch, In the diagram that top wire is voltage to stop switch, notice the wire color. The bottom wire is voltage from stop switch when you press the brake pedal, to stop lamps. The D in diagram, I believe, goes to multifunction switch for lower brake lites. The high mount brake lite isn't wired that way. hope this helps, a little. good luck

just to add, you can use a test light to check for voltage.