OK, Here's the different but happy ending to my power hitch jack story.
Removed the power head from the jack, took off its cover, and after
looking at the docs and the guts awhile, the problem was obvious:
the gear on the drive shaft was not meshed with (nor could it be made
to mesh) with the gear on the limit switch. Sent the powerhead to
dealer with a note, they replaced the limit switch assembly, I
re-synced the jack and power head, and everything works fine now.
The Airstream manual, at least for the 2004 Int'l trailers, only
reproduces a less-than-useful couple of pages from the hitch jack
docs. The full version is available at
Quick note on how this thing works: The power head has no idea of what
the actual position of the jack is. It uses a limit switch which cuts
power to the jack at each end of its travel, one for extend and one
for retract. The limit switches are activated by a mechanism driven
by the jack's drive shaft, which flips the switches after the correct
number of rotations which would extend or retract the jack from one
end to the other. For this scheme to work, the powerhead must be
"synced" to the jack. Anything which disturbes the sync, such as the
gears not perfectly meshing, will cause the jack to stall at one end
of travel or the other, which immediately blows the fuse.
Hope this helps someone and thanks as always,