Sorry, don't have any knowledge based help to offer, but here is a link to the adapter listed above:

http://www.harley-davidson.com/gma/g...bmLocale=en_US

 

Did a little looking in the service manual. The Data Link used by the dealer for diagnostics is in the electric panel.

There is a loose accessory plug located in the wiring under the seat. It has a empty plug which looks like the plug ends on the accessory adapter pictured in the link above.

 

The diagnostics plug is on the outside of the electrical caddy. There is a plug behind the electrical caddy used for the optional siren. Under the seat is a two wire 12 vdc plug. I think it is not switched and is hot all the time. I will check it out later and post.
I have a 2006 Low Rider.

 

As stated above, there is a factory supplied accessory plug on 2004 and later Dynas. The plug is found under the seat. It has 4 wires leading in to it and a weather cover snapped into the end of it. Terminal #1 is orange/red and is a source of switched power fused 15 amp. Terminal #2 is red/yellow and isenergized buy the break light switch. Terminal #3 is orange/red and is the same as #1. Terminal #4 is black and is a ground. The 15 amp fuse is shared by the orange/red wires so you can only pull a combined 15 amps from the 2 wires.

You can buy a Duesch connector fron the dealer that plugs into the accessory connector. You have to buy the plastic housing, terminal pins, a clip piece and seals for the unused terminals. You need to be able to crimp wire into terminal pins but it is not as bad as it sounds.

If building an adaptor up from scratch isn't what you want to do, you can go to the dealer and buy the cigarete lighter adapter kit for I think $25 and cut off the lighter part and splice your wire for your GPS to the wire for the lighter.

 

Thanks for the info guys, I knew there had to be an easy approach to this.