Thanks Paul, for the reference to Cruiseman's Garage.I have continued to pursue a design that will work for me. I picked up a Bikemaster Accessory Socket that is priced considerably less than the OEM part. It came with a Deltran Battery Tender type of tap with ring terminals and inline 10A fuse. I will connect the 12V accessory socket to the battery so that I can have the full 10 amps if I ever need it. I won't power my Garmin with this 12V 10A (always on) socket. Instead, I will use the switched accessory plug that is provided in the locking glove box, since it is switched off by the ignition key. I will use the Deltran USB Charger to power my handlebar-mounted GPS, and I'll keep it tucked safely inside the locked box. (I need to confirm that the Deltran unit will be able to push the 2 amps needed by the GPS model I have.) I will run a USB cable from the Deltran unit to the handlebars where the Garmin is mounted. I think it will make for a neater installation than I could have accomplished using the factory design.
I got the Deltran USB Charger for under $10 and the Bikemaster kit for under $15. This is much less costly than the OEM ($100) and more versatile.