brake and blinker problems

I have a 94 s-10 blazer and my left rear brake light and blinker dont work for the most part, I replaced the bulb but still the same thing, but yet if I take a screw driver and tap ont he screw it starts to work, it doesn't happen when I tap on the light, I checked for bare wires that could touching inside, but nothing...And after I tap on the screw it only will work for a certain amount of time..any thoughts on what the problem is, and also I was looking for the ground wire but I cant seem to find it....I have had many problems with my blazer and 60% of the time I find a loose ground, any help??

there's a ground wire hooked up there somewhere, and it's probably loose or dirty. I guess that you'll just have to look again

look on the frame rail behind the rear tire and inside towards your spare...should be right in that vicinity...

definitly check the ground wire