Well, sounds like your making progress.......I think!
Many of these issues are probably related and I would work on one thing at a time, starting with your taillights. The bulb sockets should be making physical contact with the housings, and the housings, through the mounting bracket, to the bed. If the truck has been painted, they can't make a good bond so often times a seperate wire to a good ground from anyplace on the housing will do the job. When grounding to anywhere, clean the mounting surface with your angle grinder or a wire brush to make sure of a good ground. And sometimes the bed won't be grounded to the frame so a simple ground wire hidden somewhere can get that job done.
Sounds like a similar problem on the front turn signals.
Keep working, and keep us posted.
