It should have a boost sensor which attaches to the inlet manifold and the wiring marked yellow on the diagram plugs into the sensor. Boost gauges rarely have tubes running to the interior of the car.
I've seen many ebc's using boost selenoids, but I haven't seen many for boost gauges yet. The only boost gauge I've come across that uses a boost sensor was the dual digital SPA gauge I used a while back. Besides I think Defi and Speedhut, other gauges still have direct vacuum sources to the gauge.
OP: I think you're getting confused about wiring when looking at the diagram you posted is because that's the install for a fp gauge. Either way though, wiring should be very similar like all other gauges. All gauges must have an ignition power source so it turns off when the car is off and turns on when the car is on. Then it also must have a dash light signal so at night when you turn on your headlights, the gauge light up. Typically the dash light signal can be taken from any of the dash buttons that light up at night when the headlights are turned on.
Canadians, may not have to do much searching since their vehicles all come with mandatory day headlights.