on 65-66 cars, the light switch is under the hood, on the MC/distribution block (activated by pressure). In 67, it became electrical on the brake pedal, activated by closing a contact switch (switch contacts the MC pushrod). Its kinda nutty, but check under the hood around the MC/dist block there to see if you see a switch (small box with a single wire coming from it). I wouldnt even suggest it for a 67, but then I wouldnt guess you couldnt find the brake wires under the dash, either. They just dangle there, usually getting in your face while you try to work on something else under the dash *lol* Sounds like your PO really humped the pooch on a previous brake 'modification.'
Regardless, you have to have brake lights. IF you cant find it, youll have to install a switch one way or another to get functioning lights, if they arent working now.