Just wanted to post an update as to how my heated jacket has worked out. I wound up not using any sort of variable heat control, just an inline on/off switch. Thus far the choice has been moot, since the jacket has not gotten too hot for me, so I haven't had any need for the ability to dial it back any.
I used a fairly lightweight jacket that is intended for cross-country skiing. Not a lot of insulation; it's essentially an outer shell meant to be used over layers. It has a mesh lining throughout, including the entire length of the arms though, and thus I figured it would be well suited for the project in terms of being able to distribute the wire the way I wanted to.
I used about 40' of 30 AWG wire. 6 strands up and down the front, four strands in each arm, and 8 strands in the back. So far, it has not really worked as well as I had expected. Using it by itself under my Aerostich suit really doesn't keep me any warmer than just wearing a heavy fleece does. On days I've ridden in temperatures from 35 to 45 degrees F, I've also used a fleece jacket between the electric jacket and the 'stich. A bit of a hassle, but less hassle than wearing long underwear and having to change out of it in the bathroom when I get to work. It is kind of bulky though, and I'd prefer to be able wear just one jacket under the 'stich.
Since I wasn't satisfied with the amount of heat that the jacket was producing, I reduced the amount of wire in it by a few feet by taking some out of the back. This has not seemed to increase the amount of heat significantly, so I may try to reduce it some more and see if that works. I think right now I'm down to about 34 feet of wire, based on the fact that my multi-meter indicates that the jacket is producing 3.4 ohms of resistance.
While my body hasn't been really cold with the electric/fleece setup, the biggest disappointment was in my hands. Loads of people on this forum and others have sworn that if you keep your body core warm, your hands will be fine. Well, it don't work for me, Jack. My hands still get cold, and I have hand guards as well. Since I have over half a roll of the wire left, I'm trying to figure out how to make some heated gloves or glove liners next. Eventually, I think I'll have this worked out so that I'm warm enough with minimal extra layers. It's going to take some extra tweaking, though.
Hope this helps anyone who's thinking about trying to make some heated gear.
You learn something new every day if you're not careful.
"When you have to shoot, shoot, don't talk."
Tuco Benedicto Pacifico Juan Maria Ramirez, otherwise known as "The Rat."