Check out Ttabs mod shop on Dootalk, he shows a wiring diagram.
You'll need to find the high or low beam and tie into one of those then you could probably just tie into the handwarmers ground since it's easy to get to.
If you don't have the headlight anymore I'd keep those lights on ALL the time to use up that extra juice so you don't fry your system.
I got rid of my hi/lo and hard wired the low beam because sometimes I'd bump the button and it would shut the lights off.
If there mounted to your bars you should be able to tell if there on or not though, mine are where the headlight used to be so it's a little tuffer to tell.
