I think in an older thread, someone responded that for the heated grips to work properly, the left side needed to be insulated from the metal handlebar. If not, most of the energy used to heat the grip would instead be transferred to the handlebar. Result - the left grip would never be as warm as the right. The explanation sounds logical. The right side is already insulated from the bar because the nylon throttle twist grip acts as an insulator.
This individual's solution was rather neat. He suggested purchasing another twist grip from Triumph, slipping it on the left bar, drilling a small hole through the nylon twistgrip and the handlebar, and using a pop rivit to keep it from turning. This serves two purposes:
1. It acts as an insulator for the left handgrip.
2. In the case of adhesive-backed heated grip kits, it allows
you to easily remove the twistgrip and heater in case you
want to switch handlebars.
You'd need to trim off the nylon section that sticks out from under the handgrip that actually holds the throttle cables.
More/better detail is probably out there somewhere on one of our forums.
I have a kit I purchased from Aerostitch (US company) that I have not yet installed. Probably later this year. Also need to find old thread that explained how to attach the grips to a switched connection on the wiring harness. (you do want to do that so you don't forget to shut them off and discharge the battery).
Link to Aerostitch website
Bob