I'll save you the trouble shooting details, but the "problem" turned out to be in the magnetometer harness. About 4 wks ago I bundled both the magnetometer harnesses into a "snake skin" cover so I could run it as an intact harness into the back of the airplane. I had wrapped tape around the ends to make a point so I could feed it through bulkhead holes.
You see where this is going..... I had completely forgotten that the harness ends had pins already crimped on, so all the connector pins at the end of the magnetometer harness were shorted together!!!
Once I untapped the pins so they weren't touching, the EFIS boots up normally with the full D-Sub harness connector. The only thing is I get an AHRS failure on the boot up screen, which I assume is expected as the magnetometer is not hooked up yet. When I acknowledge it, the PFD screen comes up with the tapes on both sides. YEA!!!!!!!!!!!!!!!!!!!!!
