Brake lights don't work except window
check that the bulbs are good- check that the holders, the sockets aren't rusted- check that there is power in the wires that lead to the bulb sockets- check the fuse- check, check, check, check
if vehc. uses same bulbs for turn signals as well, could be turn signal switch. The brake lamp circuit may pass through switch, to be able to change brakelamp to turn signal.....
Search Mercury Grand Marquis Questions
Are you a UK consumer? CarGurus now has a discussion forum in the UK.
Mercury Grand Marquis Experts