I figure I am not the first one to hit this little problem...
The Gerbing directions say:
Today the snow and rain stopped enough to go for a ride. I read the directions on the ÔÇ£Portable Temp-ControllerÔÇØ and followed the instruction to have engine running when connecting. Went for a ride around the neighborhood and noticed I was not getting warm. The LED was not blinking on the controller. I went back home and checked the fuse for the accesory socket as the GPS had also lost power. The accesory socket fuse had blown, it is rated for 4Amps. I figured maybe I had done something wrong, and replaced it once again following the directions. Go for a test ride again and still no heat. After doing some troubleshooting, I determine that the root case is OhmÔÇÖs Law.ÔÇ£The accessory plug on BMW bikes is strong enough to power Gerbing's heated clothing. We sell a modified BMW plug that replaces the battery harness for your connection to your bike's electrical system. This modified plug connects to the BMW accessory plug-in on one side and Gerbing's thermostat or on/off switch on the other side.ÔÇØ
OhmÔÇÖs Law states that Power (or Watts) divided by Electromagnetic Force (Volts) = Intensity (Amps). I did the math with 77W and 12V and it indicates that the fuse must be rated at approximately 6.5Amps or more than 50% larger. I checked my ownerÔÇÖs manual for my R1150RT and it does indicate that the accesory socket has a 4Amp fuse.
So at the moment I am still cold. However the legs were nice and warm with the HyperTex Overpants.
Anyone else hit this problem? Is the only solution to wire it into the battery?
I figure that if the BMW vest draws 70W it must have a similiar problem.