I think they are electric. The back of the gauge only has 2 wires, and no vacuum nipple. I think it's specific only to S15's too. You can use the holder in S14's though, but you have to cut the top bit of the plastic to fit.
Wanna ask, based on the picture, which water line will be the inlet for water into turbo? and how about the oil line also? is the one showing in the picture is the inlet for oil? or the one at the bottom?