Try buying one from Ford.

The trick is getting one that is of good qualtiy.

Obviously, the one you are buying at that store aren't. Go elsewhere,
like the dealer.

Jeff

  Don't give up yet.  It was the switch failing but something else is
killing it, they don't fail that fast without another reason.

 It might be the right switch but you are adjusting it wrong.  Or the
car has worn and you need to readjust, not just put it back in the
same place.

If the switch is the screw-in plunger style and adjusted too far down
on it's threads, when you release the pedal the switch is also trying
to be the mechanical pedal stop, and they won't take a beating like
that for long.  That type needs to have the plunger pushed in all the
way just as the pedal is up hard against the up-stop bumper so it
doesn't 'overextend' the brake light switch when you slide your foot
off the brake pedal and let the return spring pop it back up fast.

 When at rest, you want to screw the switch in till the brake lights
just go off, then only two or three turns more so the stop lights
don't blink.  You want to tap your foot and get brake lights, but let
your foot off very gently and they still always go off.  If you adjust
the switch in too far, that's when the mechanical failures start.

 There might be a rubber bushing (to pad the stop pedal arm when you
release the pedal) that is either missing, petrified, or worn.  Look
for an empty hole - those bumpers are all rubber that look like a
mushroom, the 'head' is the pad and the 'stem' holds it in the hole.

 Or it could be that the pedal pivot (where the top of the pedal arm
hinges) is getting worn and has shifted, and is putting side loads on
the switch it wasn't designed for.  If you get lots of creaking or
groaning noises as you work the pedal, the bushings in the pedal box
may be going or gone.  

  --<< Bruce >>--