Heat shrink sleeving. The basic heat shrink is irradiated polyolefin. It is expanded to 2X diameter by some kind of radiation that crosslinks it. Allows it to be expanded and then recover, actually in length. When reheated it can "shrink" to 1/2 the installed diameter. Try to size the heat shrink you buy to not be too tight on initial assembly. It is possible, but not real likely in our trucks, that further heat from some after install source, will split it open. There are other shrink ratios now as well as adhesive lined. Good stuff. I have started using solder butt splices when a splice is unavoidable. They also shrink on the wire. A little sketchy in that you have to push the stripped ends of two wire together axially. You MUST have a heat gun with a wrap around nose for those. When solder melts and you remove heat, don't move for 15 seconds or it will sag in a crooked heap. A soldered splice is the best way if you have to splice. I do use the good old blue crimp jobs too. There are places you have to butt splice or T splice. (3 way)
