My experience has been with a Garmin Zumo. I know, this is not an answer to
your question, but might offer some insight. The handlebar mounted cradle for
the unit is wired directly to the battery. Ran a garmin, fused, power cable
from the cradle, under the tank to the battery. An SAE connection in the loom
stashed under the faux (spit) left side air cleaner cover allows me to
unplug the power to the cradle. Never had a problem with hot wiring
the garmin. I used to unplug the power cable but stopped doing that a year or
so ago. I also ran next to the power cable an audio cable for the mp3 player.
Now regarding why I wired it this way, well, I was lazy. I couldn't see much
point in wiring to power up when the ignition was energized. The zumo has a 4
hour+ battery life, so having the cradle being hot all the time is not an
advantage in being able to use the unit with the power supply dead.
Hot all
the time? Heck we have a plug already that is set up that way: The Auxiliary
power socket plug. And if your choice of a GPS unit requires power in
order for you to use the GPS device, well that blows. Or will when you are
trying to use the GPS with the bike turned off. Trying to find waypoints, lay
out a route, load a saved route, etc all while the bike is running or at least
has the ignition circuit energized? Seems to me that a full time power supply
would be the way to go in that instance.
When the zumo is in the cradle, it's batteries are being charged. Should the
cradle power supply be disconnected this will not occur. Nor will the zumo
play mp3s. Not that I listen to music with the bike turned off.
In summary:
I ran a power supply under the tank. Zip tied it to the top tube. Ran it under
the frame's 'Y' to on top of the air box, then fished it back out the left
side using an sae connector between the battery and the cradle under the air
breather cover. Zipped tied the excess cable on the air box to keep it from
being sucked into the bellmouth (or into the snorkel-Vera Lynn) Left enough
slack at the handle bar to allow steering stop to steering stop movement. The
Audio cable runs the same path. I left enough length to it to allow a behind
the left leg wrap over to connect to the ear buds. Behind the leg keeps the
audio cable from coming in contact with the tank. That cable gets stuffed
behind the air cleaner cover when not in use.