I think I know the answer to this, just not the quickest way to fix it. The left tail light of my 40 doesn't work. I put in a new bulb, and the turn signal, flasher, and brake light all work, just not the running light on the left side. So what does that mean? A break in the wire or a loose connection at the fixture? I haven't had time to take the fixture out and check it. It's a fairly new replacement fixture with no rust on it. I did put a voltage tester on the socket and the needle jumps when I touch the contacts with the lights on.