I have taken the car to the mechanic several times. He get the brake light working but it only last for a few weeks. Sometimes all I have to do is jingle the wires and it starts working again.

Turn the light on and stick the prong of a voltage meter in the wire in different places following it back until there is no voltage. That is where your short is.

look for a plug close to where you can jiggle the wires to make them work, check the connection, it might be loose or dirty.

Try E-Bay.