I believe the brake lights go thru the multi function switch....aka turn signal switch.....so they can work properly with the turn signals. I will bet your multi function switch is bad.
Panama City, Fl.
I wake up in the morning with nothing to do and by supper time, I have half of it done.
2000 Lightning, s/c, tuned, Basanni, built tranny
Sold them all.....
Previous Mustangs:4 - '66 Coupes(silver/blue/grey/red) '87 GT HO, '00/'02/'07 GT Vert(red)(grey)(black), '68 Coupe, '11 GT/CS, 08 GT Vert