I recently installed a set of $20 under grip heaters I got from Rocky Mountain ATV on my 990 ADV. They have a simple hi/lo toggle switch. I wrapped electrical tape under each to insulate them from the metal bar on the left and G2 throttle tube on the right. On top I put a pair of regular moto grips. Everything went on perfectly ( isopropyl alcohol as a lubricant) and the heaters work perfectly. So far I have ridden in temps around 30F with comfort in my regular gloves. I'm pretty happy with the whole process especially the price. I spent a lot of time researching grip heaters and finally decided to just go cheap and see what happens. So far so good.
"If yer gonna be dumb you gotta be tough."
2005 KTM 450 MXC
2008 KTM 990 Adventure
2008 KTM 300 XCW