How to trouble shoot water pressure gauge

[tgorsuch]

I have a 99 Stratos. I took the dash apart and made new panels and when I put it back together the water pressure gauge won't work. Does anyone know how these things work? It has a plastic line from the gauge to the engine, is it vac or pressure? I assume pressure It is secured to the gauge
using a tie wrap.

Thanks for your help!
Tgorsuch