I would suggest that you run your SP 26xx from a switched power source, not directly from the battery.
Reason is that the metal tabs on the 26xx power cord are exposed, whereas with the SP III and other earlier model power cords, the pins were concealed within plugs.
Nothing horrible will happen if you hook up the power cord directly to the battery and the exposed tabs happen to short out across the handlebars - you'll just blow the fuse. But, this could be a major PITA if you don't happen to have a spare fuse available, or you have to remove tons and tons of baggage, body panels, etc. before you can get access to the fuse.
I have always wired my SP's through a switched power source - my Honda ST1100 has a single 5 amp accessory power terminal, I use this to operate a relay that supplies 30 amps of power directly from the battery to an auxiliary bus I have installed in the back of the moto. All my other junk - GPS, heated clothing, power outlets, hot grips, Hella horns, PIAA 910 lights, etc. run off this switched auxiliary bus. If you're serious about long distance riding, this is the only way to go. I've posted a photo of my aux bus installation below. When I turn off the ignition, the relay powering this bus opens, and all the power to this bus is cut off.
Another advantage of having an aux bus is that if you get stuck by the side of the road with an electrical problem, you just pull the main fuse feeding the aux bus, and your moto is now back to original factory conditon. You don't have to worry about dicking around with the manufacturer's wiring harnesses.
Garmin makes a motorcycle specific power cord for the 2610, 2620 and 2650 GPSR's - here's a link to look at it:
Garmin Part Number 010-10495-00
PanEuropean
Auxiliary Power Bus on Honda ST1100