Q: Intermittent problems with electrical system

The first problem I’m having is the driver’s side brake light which works sometimes, but not others. I’ve changed the bulb several times. Also, when I turn the passenger side turn signal to “on,” they both flash. The driver’s side works fine. This problem, too, is a random event. A third problem is the gas level meter. It does not show the proper gas level. Sometimes it bounces past the “F” (this too, an intermittent problem). The mechanic changed a part for this third problem, but it didn’t fix it. I’m thinking these problems must be electrical. I need your assessment and diagnosis before I go to another repair shop.