first of all ur third brake light is inside of the car or u talking about one that in the spoiler?
if ur 3rd brake light is inside of ur car (right behind of rear windsheld) there are possibility of light bulb is burned out or wire..but most time light bulb (99%)
if ur 3rd brake light is on ur spoiler (LED) your ground or power wire ripped.. it usually happend to camry or SC because from factory when they make it.. the wire is too short and they tied 3rd brake light wires with trunk support. (L shape) so after u close and open several times automatically the wires rip.. it's really hard to explain ... (i'm not good at english~)
anyways~ first u gotta open ur trunk and get the black clothes out then u will see the gas tank..
if u see right side then there are green and black wire together.. (look carefully)
check those wires out i'm pretty sure one of the wire has been ripped..just get a extra wire and connect them.. that's it...
i had same problem.. and i fixed it..it's so easy to fix it.. so good luck~ ^^