When you in stall your pyrometer the ground need to go to the motor not to the body or frame in the cab. This is something that is not in the how to paper. Just so you know. This was the problem with the jump needle what I had.
Making my brain hurt thinking about how hooked up my Autometer pyro gauge. I must have done it right because it works fine. My boost gauge is still bouncing though, I am thinking it is either the gauge or I may have a small leak in the manifold where I tapped it for the pyro. I haven't really had the time to diagnose it.