93 sable electrical problems

we have a 93 sable that all of a sudden is starting to have lots of elec problems. it started with the radio not working then the rear window defroster stoppen, now the turn signals wont work, now the interior dome light wont come on>??? all of these problems didnt happen all at once and I have checked all the fuses under the dash and all are fine? Can anyone guide me to what to check next???

thanks in advance for all the help
AL