Mojobean, here's my husband's response to your question:
Some notes regarding power hatch release:
-The power supply can be switched or on
battery power. I it's switched you will
have to turn the ignition to "on" or
"accessory" before the release works.
-The fuse rating is usually determined
by finding the current demand of the
circuit and multiplying by 1.5. If
you use 14 gauge wire for everything
except the switch and a 20 amp fuse it
will work without issues.
-The wires from relay pin 86 to the switch
and the switch to ground can be much thinner
(16 or 18 gauge) as they only carry 1/4 amp
or so. The smaller wires make easier to hook
to the switch also.
-I would recommend that the solenoid ground
wire be brought back up the hatch and grounded
to the body of the car. Hatch hinges are not
really good conductors of electricity. If
you do ground to the hatch run a ground strap
(14 gauge) from the hatch to the body to
provide a reliable ground.