I'm done freezing my arse off every winter so I had to give this a try. Everything you need should be available at Radioshack and Walmart.
I've heard of people sewing wiring onto a garment, but that seemed rather labor intensive and I'm not so skilled with sewing. I decided would try a different route, so I went by Savers and picked up a $5 windbreaker jacket with an inner mesh lining. I thought this way I could just weave the wiring through the mesh holes. At first I was going to just go the vest route, but I later changed my mind thinking I may as well have heated sleeves too. So I went by radioshack and got some 30awg teflon coated copper wire, some 16awg wire, battery connectors, 1/4 mono jack and plug for a "quick-disconnect" between jacket and bike, fuse holder, 10A fuse, a lighted SPST switch, and some heated shrink tubing. Total cost of materials came to around $50.
The resistance of this 30awg wire is about .1ohm per foot, and I went with about 30 feet to the tune of 3ohms of total resistance. Being that my motorcycle is 12 volts, 12 divided by 3 = 4 amps of draw. I went ahead and got a 10A fuse in case I decide to add heated pants or gloves later on.
I turned my fancy $5 jacket inside out and began threading the wiring through the mesh holes. I put the majority of the wiring in the chest and the anterior part of the sleeves since that's where the wind will hit me. I made sure to start and end the wiring near the same point to make adding connections easier.
The wiring is pretty difficult to see in this photo, but it's there. Once I was done placing the 30awg wire, I soldered it to larger 16awg wire and then (using fishing line, haha) stitched the bigger wiring into the jacket to secure it (in case I forget to unplug after getting off the bike) to prevent tearing.
Here's a better shot of the wiring.
Once the jacket was done, I put together the fuse holder and battery terminals and with the help of a dremel tool, mounted the switch near the left passenger foot peg.
I've been wearing the jacket inside out to keep from burning bare skin, but I plan to attach a long sleeve tshirt to the inside to better insulate the heated wire and to wear it correctly.
The jacket puts out a decent amount of heat with the bike idling and the draw from the jacket doesn't seem to affect anything else on the bike like dimming my highbeams. I busted out the multimeter to be sure. I tested the bike while idling with the jacket on and with my USB port charging my cell phone and voltage only dropped from 14.4 volts to 14.1 volts.
I don't know why I didn't do this years ago!