Brake light wiring question 65

[biohazardbill]

When I got this truck the rear wiring had been removed. I have the truck down to the frame and am installing rear bolt in c-notch. I did not see a spot where the brake lights grounded to the rear frame. Maybe I am just not seeing it or maybe they arent grounded there, so the question is where do the brake lights ground? I need to know because if they do in fact ground to the frame I need to leave some exposed metal between the notch and frame so not break continuity unless someone else has different ideas.