I have just fitted a second hand ECU, and found a black box piggy backing the green, silver striped wire to the ECU it has a live, earth and 2 signal wires one coming from the loom and then one going into the ECU. I have a pic but dont know how to post it.
any ideas please.

 

Probably it's a fuel cut defender, to bypas the normal fuel cut so that you could reach higher boost than standard....

Creepy

 

I am was still hitting the fuel cut at 14.5psi with this in, is that right?