How can I convert the 12v to 3v with enough amps to run a set of electric feet warmers. They go in your shoes and run off of a 3v battery pack. The battery pack is only good for a few hours, so I want to hard wire it into the ATV electrical system.

Possibly a wire wound resistor?

 

I would use a **** type rheostat. That way if your feet get a little toasty you cn turn it down. If they get cold you can give it a bunch of juice. Radio Shack should be able to fix you up.
BTW, I would "think" these type of socks can take way more juice than 3V. In other words they are not too voltage sensitive.
Great idea BTW.
Let us know how it turns out for you.

 

A wirewound resistor would work but don't know what value. Would have to know the current draw. Can get an adjustable one which has a sliding band on it. Again depending wattage could use a potiometer. Am thinking that since it is battery powered already it can't draw much current. I would use an LM117 or 317 which is an adjustable regulator but this would require some soldering. Have made a few power supplies using this.

I know that you already have the warmers BUT I see that they also make them in a 12 volt model from a few manufacturers that are ready to be tied into your system. Might be more effective to go that way. They make lots of 12V heated clothing. Pants, jackets, gloves, socks