One of the greatest add ons for bikes - heated grips. I use them a lot but in really cold weather use heated gloves as well.
Wire them direct to the battery but via a relay that takes switched power from the ignition or other circuit which is energised by the ignition i.e parking bulb. The relay takes miniscule amounts of power to trigger so pretty much anything will do.
As usual with adding electrical items you need to make sure your electrical system/alternator is up to the job and can provide enough power for the normal bikes electronics to function as well as the add on's. I would expect a set of heated grips to be 40-50 watts (it will say on the packaging) so thats about a 4amp current draw. Make sure there is an in-line fuse of slightly greater value than the actual amperage and that that is fitted as close to the positive terminal of the battery as you can get it.
