As promised, albeit a little late, I fitted a set of Symtec grip heaters on my KTM 640. Bought the kit from Winding Roads, who appear to be the only UK stockist, with the metal toggle switch instead of the plastic rocker.
In all, fitting probably took half a day, but as I kept getting interupted by people calling round I only finished it yesterday lunchtime.
You need to have a new set of the grips of your choice, unless you want to risk removing and refitting the old ones. I didn't and sliced my old grips off with a stanley knife. The elements are embedded in a plastic sheet which has adhesive on one side so sticking them on the bar/throttle tube is a doddle, they are marked for which side. Have a good look at where you position the throttle side before sticking down, as you have to be able to use the twistgrip without the wires fouling anywhere. Fitting new grips is next, and everyone will have their own method. I put a set of Pro-grip "Rally" grips on, which are a bit fatter than I would normally use. If I don't get on with them, they can be carefully cut off and replaced with my usual "798" grips. My favoured method is to spray brake cleaner inside the grip for lubrication, then slide them on quickly before it evaporates. With the added thickness of the heaters under them, the grips seem to be stuck fast. If not, I usually lockwire them on anyway.
After cable tying the wires along the bars and up to the dash, I used the spare accesory socket on the 640 to power mine, but the kit comes with a splice connector for them to be powered off a headlight wire or suchlike.
HTH
Mark