Put a relay under the headlight mask that is connected straight to the battery.
Connect your grips to that, have the relay trigger by acc2 ( that is the switched one IIRC, only powered when the bike is running).
This will eliminate the load from the stock harness, your grips will perform better since they will draw straight from the batt. I used a 12ga wire for the relay so there is as little resistance as possible. I also power my LED driving lights off the same circuit.
You can see it on the left side in the picture with the blue wires. The bundle is bulky due to the connectors for the LED's