hey i have 1998 ford 150 5.4l and im trying to install a vacuum gauge in the cab. My question is where the hell is the vacuum line where im supposed to install the tee for the gauge to get its reading a picture would help a milllion percent !!

 

There isn't one because the engineers never supposed you'd install a vacuum gauge. You'll have to run one yourself from the intake manifold, or one of the larger lines coming off it. Find a grommet to bring it thru the firewall & route it to wherever you put the gauge.

Mine had one for the old vacuum cruise system (which I upgraded), so that's what mine is hooked to.
.