Pressure actuator (as nature intended) = wastegate is normally closed. Manifold pressure overwhelms the spring and pushes the wastegate flap open so some exhaust flow bypasses the turbine which reduces compressor rpm.

Vacuum actuator (the devil's own work) = wastegate is normally open. Government commission determines when wastegate should close to allow exhaust flow to turbine which increases compressor rpm.

For a preview of what you're missing, rig a line directly between the engine vacuum pump and wastegate actuator. That'll effectively wedge the wastegate closed. Go for a drive keeping in mind that there is no mechanism to prevent an overboost situation. C'mon, it's a T25. It's not going to produce more than 1.1 bar long enough to destroy the engine unless you try to climb Pike's Peak at WOT. Just don't hold the pedal to the floor and you'll be fine during the test.

The nipple for the ALDA signal line is 603 098 03 04 with washer N 007603 008109 or any crush washer that'll fit. That said, I don't know if the other ports are tapped with the same thread. Jeremy can answer that if the ports are the same between the 602 and 603.

I don't recall that anyone who cleaned the intake manifold noticed a performance improvement for the effort. Sure feels good, though

Sixto
87 300D