Don't bend the metal or shim the plunger. In case anyone doesn't know how to click on a link, here is how to adjust the brake light switch:

Give the whole thing a twist counterclockwise to undo the clip. Once you have it off, pull out on that black plunger till it is about 3/4 in. out. (Pull hard, it will make a ratchet sound as you pull out.) Put the switch back on by a clockwise twist in the square hole on the bracket (the brake pedal should be down when you put the switch back). The brake pedal will push the plunger in some, but not all the way. It is self adjusting and should now work normally if this was the problem.