Splicing wires in rear hatchback door wiring harness snorkel loom

Like MM said, and also twist the wires together "inline",  like the url  shows at the start of the video but soldered first, not twisted like for a wire nut.

I know all the other words but what do you mean by snorkel loom?

Solder connections are the thinnest, if you get pretty good at it. If you haven't done much, practice on something else. Make sure the work is hot before applying the solder and it should melt and take barely any width other than what the wires themselves take up. If you scrape the wire ends with knife first, and twist one wire around the other, end to end, the solder will stick right away, and the soldered part only has to be 1/4" long if that is an issue. Put shrink wrap on the wire before the second soldering!

Even if you don't use the perfecly flexible wire, it last for ? years the first time and will probably last almost that long this time.

I doubt anything uses more current than 20 gauge will handle. In my limited experience, up to 1995, American cars had thick wire and Toyota had thinner wire. My guess is that after the war, the Japanese were econmizing in wire and saw no reason to stop.

I guess a better term may be "rubber wire harness sleeve"

Or maybe "automotive rubber wire harness grommet"