Well, this isn't exactly about an 18 wheel truck, just a International 4300 DT466 box truck. Thinking it is about 15 years old. Have an issue with the rear brake and turn signal lights on the driver side. Sometimes they work, sometimes they don't. Every morning when you first start the truck, they will work, however, after about the first or second time you use the left turn signal or hit the brakes, they flicker and stop working. My first thought was a ground issue, but, I can simply turn off the truck and then start back up, and they will work for a while. They quit again after a couple of times using brake or left turn. Hoping someone can give me a good starting point on where to look.