May seem like a noob question, but then I am pretty new to turbos...

Anyway, I was looking at this one on eBay
http://cgi.ebay.com/ebaymotors/B-TURBO-BOOST-CONTROLLER-350Z-G35-240SX-S13-S14-MR2-GTI_W0QQcmdZViewItemQQ_trksidZp1742Q2em153Q2el1262QQcategoryZ33742QQihZ006QQitemZ160294446980

and I'm wondering what the little 3-port cube thing is for.

My understanding of a turbo boost controller is that you install a pressure regulator between the intake manifold and the wastegate actuator to make sure the wastegate stays fully closed until the pressure reaches the psi level you've set on the controller - then it starts bleeding pressure through to the wastegate actuator.

So since all you are trying to do is regulate the pressure to the wastegate actuator, what is the 3-port piece for - is it even needed for a system like the one on our Mercedes?

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1984 300 Coupe TurboDiesel
Silver blue paint over navy blue interior
2nd owner & 2nd engine in an otherwise
99% original unmolested car
~210k miles on the clock

1986 Ford F250 4x4 Supercab
Charcoal & blue two tone paint over burgundy interior
Banks turbo, DRW, ZF-5 & SMF conversion
152k on the clock - actual mileage unknown