Just finally got around to installing this on my snowblower, as a pre-emptive strike against the coming winter cold. Although I didn't need the instructions, I found they were created in a way that could help the worst "welder" (one who creates sparks and welds wires instead of fixing electrical problems) install these without an issue. Drilled a hole in the "dash" for the switch, drilled another small hole in the bars for the ground (not necessary, as you can ground it to an existing bolt), ran the wires, and installed the heater elements. The resistor for the "low" circuit can be a little bulky in tight spots, but was easy enough to hide on this snowblower. Fired up the engine and it works great! The true test will be this winter though ...
My snowblower (Toro 828 Powershift) has a lighting coil, which is what I tapped into to power these grips. It produces a little over 14 VAC at full throttle, which is plenty, and shouldn't affect longevity at all for being too high. Never measured amp output of the coil, because if it can power just one light, it can power these grips. Probably wouldn't handle both these grips plus a light (don't have, or need one) just judging by the output wire size from the lighting coil (about 18 AWG).
I have this same style heater on my ATV hooked to a controller that allows 5-way temperature adjustment, plus the ability to power 3 other accessories the same way. I prefer this peel-n-stick style over the ones that come molded one-piece, so that I can keep whatever soft grips I have without having to resort to the hard plastic of the other style. With these you can keep your existing grips.
A tip for those who fight with removing rubber grips from motorcycles, ATV's, snowblowers, or snowmobiles - use a screwdriver first to break the glue bond, then insert an air nozzle to blast the grip with compressed air. Block that little hole in the back of the grip with your thumb. Slides right off like magic .. most of the time. Either way it's easier than what you were doing before!