1989 Oldsmobile 88 turn signals & brake lights

I recently took my car into a repair shop to have it serviced for the brake lights not working and the turn signal not working. They replaced the fuse (20v). It worked for a day. The next day it started working but 5 minutes into driving it stopped working again. It was 5 degrees outside (don't know if this matters or not). Is it the fuse? Is it the relay? Or is it a more complicated electrical issue? Thanks