Your bike has 12v power and is a very noisy power source for a computer system. The ignition and coils are unshielded, as well, so these radiate electromagnetic interference, which can zap or ay least confuse computer circuitry.
So, keep your voltage converter and all power wires well away from the ignition leads, and make your power tap into the bike electrical as close to the battery terminals as you can. That battery is what irons out most of the noise spikes in the electrical system of an SOHC4.
I bought my wife a Garmin Nuvi 660 quite some time ago. She has the worst time with navigation and has no directional sense. Long ago, she San Fransisco with a friend to go to LA. Got on the correct freeway and drove the wrong ddirection for an hour before realizing the mistake. She has driven 20 miles because of unfamilar roads when only five miles from home... to get home. She's actually a very smart woman... just has no aptitude for navigation.
Anyway, she absolutely loves her Nuvi, and no longer gets in a worried, stressed out state when she has somewhere unfamiliar to go by herself. The unit talks to her so she can still focus on diving rather than a map, or memorized instructions. If you miss a turn for whatever reason, it recalculates your route so you still get where you are going without much hassle. With written instructions or a map, you have to figure out corrections on the fly while negotiating traffic and reading road signs (if they aren't obscured or vandalized), and that is far more distracting than having the Nuvi simply revise it's instructions while you drive. The moving map is nice to glance at now and again, and certainly helpful during pre-trip planning. But, enroute, you don't need to pay much attention to it. The Nuvi also compensates handily for the common practice (around here) to have the same street have three or four name changes along its route.
If you live in an area that is laid out in a strict grid, and you have a compass, the Nuvi other than the built in compass, isn't that necessary. But, many areas have one way streets, and dead end streets to guide traffic onto major thruways. Further, areas in hilly or mountainous terrain can twist your heading 180 degrees without leaving the road you are on. At night or when you can't see otherwise normally appearing landmarks, the Nuvi will still get you where you wish to go, as the satellites are pretty reliable reference points. If you drive, at all, in unfamiliar territory, they can save you time, frustration, and gasoline.
She also has the SD card and MP3 storage and playback capability. It will take 4 gig cards. The FM transmitter doesn't work well in this area as there are so many radio stations in this area, that there is no room on the dial to find a blank channel. But, it works very well with a cassette converter, or a stereo with an aux input jack. It will work with headphones too, which she uses for daily walking exercise, but not in the car.
I was very tempted to get the Zumo for me on the bikes. But, they cost more than double that of a Nuvi. Still, if I were to take a trip on the bike, I think I'd spring for one.
Cheers,
