TL;DR - IT WORKED!
You can buy heated grips off of Amazon ($10), or AliX for like, $1.50. I was more impatient than I was cheap. Rushed them over for me not to work on it for a month.
They're for quads, or snowmobiles, or motorbikes. You wrap them around the grip, then they have a big piece of heatshrink you put over the bar ends and shrink it down.
Just for example:
Amazon Link
It's just a resistive heating element zigzagging back and forth, laminated inside some mylar sheets. With nothing over it, it gets scalding hot in about 5 seconds.
You can wrap a rectangle around a cylinder, but unlike handlebars, a rectangle isn't going to roll around a torus like a car wheel. So, some modifications had to be made.
I just cut between the elements with a pair of scissors, turning it into a comb.
The spine of the comb can't be cut, and it can't curl sideways, so there's only 2 places to attach it that only curl in one direction. 1 - Inside the wheel, or 2 - Outside the wheel. I put a piece of electrical tape on it and put it on the inside of the wheel. This was the wrong choice, more on that later.
Then I wrapped it with some thinner strips of gaffer tape. This was trickier than I thought it woudl be, as the combs weren't held down and the tape was going diagonally past them, so I kept having them escape and needing to be tucked back under.
The steering wheel itself is metal with the plastic molded over it, so I couldn't really aim a drillbit where I wanted to go to completely hide the wire. But I drilled a hole that came out the behind the side braces.
And I cut a rectangular hole for the switch in a place a little bit wards the back side of the wheel where the airbag wasn't interfering.
I had to cut the harness apart a bit. Lots of this wiring was not thought out, I have probably 3x as many splices as I should have had, and I STILL routed wires on the wrong side of the steering casting in a couple places. I don't think I even had a soldering iron, so, splices are literal splices covered with heatshrink. The steering wheel had a ground connector (uses it for the horn), but I didn't have any extra wire to get over to it, so I just tucked the ground wire under a screw on the metal frame.
Next, you have to decide where you're going to have the slip coupler. You have 2 choices:
1 - Around the barrel of the steering wheel/column, or,
2 - On the back of the steering wheel.
Option #1 isn't really an option in my case, which wasn't at first obvious, because the steering wheel doesn't have a constant radius. The wheel itself does, where your fingers go, but, it's a lumpy oval shape around the sides. Anything protruding out from the rear (stationary) part of the column would be snapped off by the wheel as it turns:
But the back of the steering wheel for me, was actually blessedly flat. And had a removable panel underneath to access the airbag wiring. So that was convenient.
Here's a better look. Fairly consistent gap between the column plastic and the back side of the wheel. So one side of the slip coupler will be on the stationary column, the other part will be on the back of the wheel, and some kind of leaf spring to bridge the gap.
I had some brass strips from the iside of a junked powerbar, they fit nice. And some plastic screws (tiny bolts would've been better):
Don't be an idiot like me and fold the brass before you anchor it, or you won't be able to get the screws in (bolts would be better). Also, I didn't have a soldering iron, so, the wire is wedged and clamped down and shutup, it's good enough.
On the opposite side I just heated the brass up with a heat gun and melted it through the plastic. No I didn't get it too hot, that was later.
On the inside I just folded the brass tabs over and I think put some dollarstore epoxy on them. THIS is when I got too hot, I had to solder with a heat gun and it melted the plastic. Duh. Solder the wire onto the brass FIRST before you insert it and fold the tabs over. Also I added a foot long piece of wire, and forgot the wire is already there on the inside, so I cut it off and spliced it after 2" (unsoldered), rather than try to risk melting the plastic again.
I added a head and tail wrap to the existing gaffer tape wrap to secure the ends better. It was fine with the gaffer tape, but I also added these carbon fiber clip-on steering wheel covers to hide it. The wheel gets too hot without them, and too much in the same place. You can't see the power switch, it's just slightly on the back side, by the spoke. You can reach it with your fingertip.
I didn't get pictures, but I just use a "fuse tap" ($6, autostore), that is basically just a Y-splitter for an existing fuse. It takes the place of the original fuse, and has 2 fuse slots, the original that you put back, and a new wire for you to power your new device. I tapped the accessory or stereo fuse I think (anything non-mission-critical that shuts off with the ignition). The wire itself I snaked along the plastic and out the back of the collumn.
...
And it works, mostly. Warm in seconds, never gets too hot. The "hi/low" power is stupid. High pulls 1.4amps, Low pulls 1.2amps. I think the switch just toggles in an 8" long piece of nichrome hidden in the wire harness to limit the current. There's practically no difference.
Issues/Improvements:
1 - The Honda Oddyssey wheel is so oblong, that at certain points in rotation, the entire leaf spring is exposed. On one hand that means you didn't even need to remove the wheel to screw that brass in, just rotate it to the exposed area. But it also means that it springs out a bit too far, and then crashes into the side of the wheel as you continue to turn it, and scrapes it with an annoying sound. EVERY TIME you're turning the wheel a full turn (only when parking). It also pushes it a bit sideways. It's not great. If I was to do it again, I might use a captive ball bearing or something on a spring, like how a rachet holds sockets. Or, a shorter brass strip, a half inch is probably lots, you don't need 2". Or, a different location that is closer to the steering axle so that it never gets exposed.
2 - The plastic of the column, at least on Hondas, is completely trash. Its bounces and flutters all around, is barely even constrained. You can easily flex it a half inch.
3 - The heat wrap doesn't fully wrap, and I chose the wrong starting place. It makes it maybe 3/4 of the way around. Well, it's my fingertips that are coldest, never my palms, and yet the heat is mostly at the palms and then dies by the fingertips. I would start the heat wrap on the outer edge of the wheel, not the inside if I was to do this again, and so should you.
4 - Temperature control would be nice. With just the tape it's way too hot, but with the cover on I'd like it to be hotter. It only draws 1.4 amps so there's lots of room to pull more power.
5 - Clock springs (not an actual spring, and not a split ring, it's just a ribbon of wires that coil and uncoil to get wires to your steering wheel without tangling), are just janky loose, sloppy garbage, I might not do this at all ever again. They're not even really attached properly, they rattle and shake around (the noise of you turning your steering wheel). I don't even think it's properly centered. That means that I can probably just grab the clockspring from any other vehicle at the junkyard with extra wires or a heated wheel, and the connectors off a matching clockspring to the original, and just create a splice monster. Since this only draws 1.4 amps, the signal wires alone on some random un-used thing are plenty to carry the power. Or use the same clockspring, if I was willing to sacrifice the radio controls, those were plenty thick.
