its othwise known as a boost controll valve (from that u should get what it does)

it bolts ontop of gearbox near clutch fork & there will be a 2 wire black plug on ur loom between the metering unit & dizzy.

it pipes up:

top to actuator
middle to turbo unit
bottom to bottom of metering unit

i wouldnt bother with it mate, ide just block the metering unit 1 off & put a bleed valve in between the turbo unit & the actuator. job down & now u can turn ur boost up & down as u please!