<VV> Need electrical help on tailights

[John Gull]

I am not electriclly inclined, so would appreciate any advice. I have a LM
that the right  taillight does not light up with the brakes on, but the park
light does work. I have tested the bulb to eliminate this. Also the is a new
wiring harness about 3 years ago. Tried to figure out the wiring diagram but
not knowing how to figure out. Any suggestions?  Thanks John Gull