1998 Chevy Lumina brake/turn signal lights

Electrical problem
1998 Chevy Lumina 6 cyl Front Wheel Drive Automatic

Hi, Recently tried helping my sister-in-law with a used car she purchased. Originally it appeared as if a few lights were out, but after relacing all and others that were still working, found that brake lights on rear end wont work on their own, but rear dash brake light will. Also have what I believe the turn signal switch is bad, as operating it can either work right, or cause fast operation, or not work at all depending on which way you push-pull or giggle turn signal handle. Im leaning toward the switch but not sure how it ties through with the brakes