Okay, got it. Here is what I need you to do. First, power to the parking lights comes direct from the parking light relay, seen in pic 1. From that point, it goes to all lights (Pic 2). What I need you to do is check one thing for me at that light socket. With the lights on, there should be 12v to the red wire with a yellow tracer. Check that.
Also, I need to confirm one more thing. I reread your original post. Is it the parking light that doesn't work or do you mean the brake light doesn't work when the head lamps are on.
If it is a brake light not working, check for 12v at the white wire with a black tracer. (See pic 3)
Let me know.
Images (Click to enlarge)
Saturday, October 31st, 2020 AT 10:42 AM