"A, B, and C each take one input"
versus
"A, B, and C each takes one input"
which is correct?
It uses the plural verb. You can see it more obviously if you reword slightly:
A, B, and C take one input apiece.
"each" and "apiece" are modifiers that indicate that "one input" applies separately to each item, but it doesn't change the plural nature of the sentence subject.
Correct:
Wrong: