I had a similar issue with my Nuvi 550, I could power my cigarette lighter element from the lighter plug, but not the Nuvi or the Satellite Radio either.
I asked the dealer why it wouldn't work. They took the fairing off and switched the wires on the back of the lighter plug, and now everything works from the lighter plug.
Apparently the lighter element doesn't care about polarity but everything else does.
73 Sporty - Sold
07 Sporty - Sold
09 Vivid Black Road Glide (FLTR) with ABS, Security, Fuelmoto Satge One, Clearview, Harley Hammock Seat, Hogg Chopps Lowers, Bright Ass Tail Light, SERG Headlight Bezel, Detachable King Tour Pak, Painted Inner Fairing, Cruising Southeasten Wisconsin, Delivered 3/6/2009:clap:
09 Black Fat Bob (FXDF) in Vivid Black of course, Delivered 5/1/2009