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.
Hello all i just bought a Skyline r34 Gtt year 1998. fully stock with 32k mileage only. previous owner just keep the car for collection.. cancel my deal with r32 gtsR becoz of this r34.