I think EriCal is right about the failure mode, since I've had two failed sets on my 07 Road King and the problem definitely was not in the wiring between the grips or between the power source and the grips. I did the work myself and I'm competent to do it.

So far, the heated grips I installed on my 09 Ultra have not failed, but I suspect it's just a matter of time.

Right now I'm working on a method to install Hot Grips on the Road King. The usual problem with installing aftermarket heated grips (Heat Demons install inside the bars) is that the Harley throttle grip (assuming a model with throttle cables) incorporates the receptacles for the cables, rather than having a separate throttle barrel and grip (which would permit ANY appropriately-sized grip to be installed.) Joker Machine makes throttle barrels that fit 07 and earlier (throttle cable-equipped) and 08-up (electronic throttle) models. I bought one of each and it looks like they're going to work with the Hot Grips.

Once I do the install, and assuming it's successful, I'll write it up and post it. I have used Hot Grips in the past and they work well. What I don't like about the idea of Heat Demons (and I haven't used them myself) is that they must heat the handlebar before the heat reaches the grip. That either takes a lot of power or a lot of time, or both, and seems like the wrong way to do the job, engineering-wise. Also, installing something inside the bar is problematic on electronic throttle-equipped models; there's plenty of junk inside the bar to start with.

First on my list is to install Hot Grips on my KLR 650 so that I can become aware of any installation difficulties there, rather than on the RK.

 

The Heat Demons heat up in a matter of seconds. And yes they transfer heat through the bar. I have been using these on all types of motorcycles for years without ever having any issues. I have tried the Harley Heated grips and they always FAIL! As far a current draw, they are both using the same power source and the same voltage draw.

 

I stand corrected. I thought it would have taken a while for the Heat Demons to first raise the temperature of the bar ends and then the grips.

 

+ 2 on Heat Demons. Installed them myself, 3 flawless years so far and no hint of deminished or "aging" performance.