Nicked this off a dutch forum member on xs400.com....
Top tip for a DIY heated jacket - haven't tried it myself yet but I read it works like a charm
so basically what you do is you buy some really cheap stuff at Walmart or something (here in holland at Action, Lidl or Aldi supermarkets):
- a heated car seat cover which plugs into your 12V car power outlet (the lighter plug thing)
- a fleece jacket/vest
- a little bit of thread and some nifty handwork
- another fleece vest (old, or cheap new)
- a 12V car socket to mount onto your bike somewhere
so basically you cut along the stitching from the heated seat cover to take out the part that's heated without the insulation and padding. Be careful not to cut any wires (you can usually see where the heated wires are by looking at the stitching). Now lay out your fleece vest and position the heated part of the seat cover around the back and the mid section - stay a few inches away from the zipper on the front and the arm holes. Now sew it into place with your sewing machine. Cut out a slightly larger piece of fleece from the second vest and cover the heated pad with it, sew that into place as well.
Mount your 12V car power socket somewhere into your wiring harness - you might want to add an extra switch and a fuse into it as well. Think about what the easiest place will be to plug in your jacket - probably somewhere on the front of your tank, near the dash or something.