Here's a 3rd brake light wiring diagram to peek at in this HAMB thread. Maybe this is do-able for you?
Brake light wiring with 3 wire turn signal help. | The H.A.M.B.
Don't tell ANYone, but I also talk all nicey-nicey to my car, even patting it on the dash pad after a nice job of taking us there and back. Ya just NEVEr know!!
Yes, I'm sure now the powers here might 'brand' my profile with a little 'cuckoo' 'smilie', haha
I didn't see any 1986 Crown Vic wiring images on google, but I would try for a big Ford car, no trucks, no 3dr cars (liftgates), since those have too much trim to remove to get at the wiring. Mustangs avoid because junkyard folk likely charge more, just cuz it's a 'stang, lol. ...or if that HAMB thread winds up having the info you need, better yet!!
Funny thing ...last night was NSRA (here we are MSRA) safety inspection night, and of course my pesky l/rear brake light decided it was gonna act up. ...Christine again, hmmm? ...So a buddy and I frantically checked this and that, all while the inspector cut me some slack and waited patiently --turned out to be the lower bulkhead connector just a teeny bit loose, and wal-la, it came to life, and the car passed, yay! So yea, 'car karma' --it's verry real!
Knowing my car so long it does seem to have a 'i'll show you attitude' or possessed sometimes. In '78 i commented (and remember AM was the main radios then) that the best thing bout the car was the radio and air shocks. Right after that BOOM!
As for your lights, i would think that should be good enough, they are definitely visible! Next time i'm junk yarding i'll check some of the cars and see what they got in there, if i can figure out what i'm looking for. Retrace the 3rd light wire back. Thanks for the tip!