I just skimmed the last page, and I'd definitely wait for avionic to confirm before trying this - but if these aren't important pieces and you can't find the failed trace - could you just run a jumper wire from "neg. lead of C509" to "L4" - even just to check if it brings the lights back to life?
At least it'd confirm if there actually is a break somewhere.
I wouldn't try that until avionic confirms though, I may have missed something obvious on my skim.