Fitting heated grips

[Punkstig]

I had my previous ones fitted on the same circuit as the fuel pump so when the ignition was off the grips were off, worked a treat.  But I think the new Oxford Hotgrips have a voltage sensor and won't turn on if the voltage isn't that of a battery being charged by the engine.

Yeah, the new oxford ones are pretty good and also turn themselves off when the battery gets to a certain level, but its still a risk.
Brake light feed is a good place as it doesn't drain anything noticeable like you've found on sidelight/headlights!
(Obviously finding the constant feed to brake lights, not the one that's only on when the brake is applied! )