(1) check for voltage at the brake switch, if yes, go to (2), if no, find fuse and trace wiring

(2) short across pressure switch, do lights go on? If yes, change switch, if no, find fuse and trace wiring.

(3) has some nimrod dorked with the steering column? Brake light wiring goes thru column circuit for turn signals.

(4) check bulb for operation/corrosion....do running tail lights work?

It's a really simple circuit!!