rear defroster

i have a 1999 mercury grand marquis and the rear defroster does not work i checked the fuses and relay and all are fine. i check the rear electrical termainals and found a voltage of 13.5 so i know its powered to the rear terminals. i also check the continuity on the strips that run through the glass and they appear ok. the defroster was working some in the past but now there is nothing.. ????? any thoughts of what else i could do??? thnaks steve

check to make sure that you have a good ground connected to the rear window strips. if you don't have a ground connected the strips will not heat.