that picture is an R33 engine bay, so it has a hose running off that nipple to the electronic unit (circled) for the boost gauge in the factory cluster.
the stagea however doesn't have that, so the nipple is plugged, simply remove the plug and run your boost gauge off that.
the boost controller needs to be inline, between the turbo actuator, and a intake pipe pressure feed, which will likely run off your intercooler piping.
i'll take some pictures tonight, as kylies has a fmic/pod/boost controller, otherwise i can give you a hand if you need it.