The voltage in each splicing wires ?

For case of injector wires harness, 18WAG spliced into four 22AWG.Four 22AWG are in parallel with 18AWG wire. Votage in 22AWG is same as 18AWG. Oviously, resistance high in 22AWG. So, the current decrease as expected. So, the current decreases by the factor of R.

No, the voltage does not appreciably drop through a splice.

Um, with respect, I think it may be a good idea for you to pick up a basic electrical book in your own language, as you don't seem to quite grasp the fundamentals? For example, in another post you didn't seem to realise all headlights are in parallel, not series. Here you seem to think the voltage drops are in the wire, rather than almost entirely across the device being supplied the electricity?

It may be a language thing, though?