The answer is....yes....a Navigator III can be attached to a 99-04 LT.
I tapped into the map light (remove windshield, and remove trim piece behind instruments) and routed the 2-wire harness around the left side of the dash. I found a 2-wire connector at Pep Boys, meant for an alternator and soldered the connector to the end of the wire. Now the bike is ready to accept the Navigator connection, but I needed to prepare the stingray to mount the unit.
In order to prepare the stingray, the little BMW logo is removed by gently prying it up.
The stingray has to be taken apart by unscrewing 6 torx screws and a few phillips screws. Underneath the logo is a sunken area that is exactly the size that needs to be drilled out with a hole saw or step bit, which I used. The GPS comes with a little plate that can be used as a template to mark and drill the 4 mounting holes. After drilling the holes, the GPS mount can me bolted to the front section of the stingray.
The wiring has to be routed BEFORE you attach the GPS mount. Now the cradle is bolted to the lower mount, and the GPS can be mounted inside the cradle.
Here is the wiring routed through the bottom of the stingray:
Here is the Navigator III mounted to the stingray:
I connected the wires from the stingray to the bike, including the Navigator connector and everything worked. The Navigator sits just above the radio display and just below the dash lights so everything is visible. My unit came with a sunshade which keeps glare to a minimum except i the sun is directly behind me.