After much searching and reading of posts, I decided to hook up my SAFC using the pressure (boost) sensor, but I am using a FCD from Mazdatrix, the kind that plugs right into the pressure sensor. I'm not really sure which wire to connect the grey wire to. I can't splice into the brown/red stripe wire because that would be after the FCD.

The four wires coming out of the plug before the FCD are black, blue, red and white. The black, blue and red all connect directly to the other plug which then connects to the factory wiring without going into the black box. The white is the only wire that goes into the black box. There are three wires coming out of the black box and going to the factory wiring plug, black, red and yellow. The yellow wire that leaves the black box connects to the brown/red stripe wire in the factory harness.

I am guessing that the white wire is the one I should splice into for the unmodified boost signal. Is that right?