Sorry about the delay -- Off from 'work' the last week, my spouse and I (42-years with the same one as of last week!) are building a retirement house.
As for why M/T's guages would go to 'empty'/'cold' at power off, I don't know; maybe his guage system has been changed to more 'normal' innards. Some folks have don't just that - and don't necessarily tell the new owner.
By the way, Old Carw Weekly just had some comments on the Ford King-Seeley guage system in their Q & A section last week. That information serves to verify my independent findings.
Thanks, JLB
55 Ford Crown Victoria Steel Top