Blue wire and FCD...
 

Looking at getting a SAFC2 for my rex. Ive read all about the s4 tsp issues, and running off the boost sensor instead of throttle %. My question is, do i tap both the throttle % and pressure wire (blue) BEFORE the fcd? i want my afc to read boost accuratly, because im not sure that my gheto autometer does...

The Autometer mechanical boost gauge should be right off the IM, so it's gospel.

You want the gray wire tapped after the boost sensor & before the FCD, so it sees the full range of signal.

I tapped the blue wire in after the FCD, so I can verify the FCD clamp point.

You could even tap the blue wire to any 0-5volt signal you want to monitor. (intake air temp for example)