Automatic Transmission Shift Lever/Plunger Problem

My daughters cabrio just started having the same problem, I took off the knob and lifted the selector panel,, there is a plastic cam that prevents the plunger from going down to shift gears. there seems to be a switch that controls the cam, I don't know what the switch does, but I jury rigged it so the cam cant slide under the plunger. She is able to now press the side button and switch out of park. again I don't know what the switch does. am trying to researc a permanet fix.

Replace the brake light switch that is actuated by the brake pedal. I've had this problem. The car thinks the brake pedal is not depressed so the interlock for the shifter will not release. About a $40 part 10 minuets to replace.