I just went to Wal-Mart boat section and bought the 12v lighter there and wired it up with a 20amp switch and fuse (I put a 15amp fuse in) wired it directly from the hot side of battery, thru the switch, thru the lighter, thru the fuse and grounded at the reflector on the side front ( I shined up around the screw hole to make a good ground).
I used a "U" bolt to hold the 12v cig. lighter (power adapter) to the right top fork. You can kinda see it in this picture.

Pretty cut and dried, I went directly from the hot side of the battery, there is plenty of room to run the wire thru the top hole.

Run the wire up the frame and across under the tank, I zip tied my switch between the seat and tank on the right side rail (with "on" and "off" written in gold paint for my wife to read and know when its on or off).

Then continued with the wire under the tank to the 12v adapter that I attached to the top part of the forks between the triple tree braces with a 2 1/4" "U" bolt. I believe I might have made the holes in the adapter slightly bigger to accept the "U" bolt.

The ground wire and waterproof fuse holder I zipped tied to the frame near the right side front reflector. I just loosed both screws, then removed the top one and scraped up the paint around the hole to make it shiney and attached the ground wire under the reflector.

Switch it on when you need it, and turn it off when you don't, I used it to charge my cell phone also, I put a block of Velcro on the front of the brake reservoir and on the back of my smart phone cover, holds it right nicely.

Its not the only way to do it, and maybe not "electrician approved", but it works outside of regular bike harness and won't interfere with power consumption.

I'm sure there are other ways to do it, I've always added power adapters to all my motorcycles, but usually I add a six point fuse box with a relay, because its the safest route to go.

With the savage using about 85% of its electrical power you don't have much room to add any extra's, that's why I went outside the harness and have an on/off switch.