depends on where you are putting your gauge. i have mine sunken in the dash to the left of the DIC. i just ran the line down through the dash on the left side. it's pretty clear above the pedals and it's easy to see if you pull the fuse cover off (lower left of the dash). then you'll see a spot in the firewall that is a circular(from what i remember) gasket(that's just what i'm calling it) that a wiring harness goes through. it's right above where the clutch is or would be if yours is auto. i poked a hole in this rubber "gasket" just in the flat portion down and to the right of the wiring harness. then when you go in the engine bay, you will see the opposite side of the "gasket" where you would pull the hose through, then just run it to where you're tapping into the vacuum line however you want and secure it.
this is all going off memory of when i put mine in a couple weeks ago, so sorry if it's a little confusing.