I used to be the same way, but 3m makes these really nice T taps that are a spade connector that I've had pretty good luck with. They are filled with dielectric grease to seal the connection once you splice them. I've had as good of luck with those as I have with a soldered T splice.

i also really like the new fusion tape they have, you wrap it around something and it forms a solid layer of rubber as it fuses to itself. Its way easier to use than heat shrink, especially on a T splice. Heat shrink can be finnicky.

As for the question about whether are trucks are set up that way, now that I think about it, i believe that is correct, that the trucks are already set up with stop turn lights from the factory. I haven't really done any work on a truck with stock lights, though, since mine has a flatbed, so I couldn't say for sure.