I've done this to a couple of my bikes and it's nice to be able to fine-tune the heated grips to just the right heat level for the weather you're riding in. What I use is a 12 volt 8 amp PWM (pulse width modulator) "LED Dimmer" that can be had on eBay for about $3 shipped. (Search for "12V Led Dimmer")

When you take the box apart you'll find that the potentiometer under the knob is separate from the PWM printed circuit board. What I did was lengthen those wires so that I could install the potentiometer and knob in the dash pad and hid the rest of it in the fairing.  I also coated the potentiometer in five minute epoxy to waterproof it.  I installed a 3mm 12V LED, wired to the output, right above the control knob for visual verification that the heated grips are getting power and to make it easier to find the knob at night.

BMW OEM Heated Grips: The factory main wiring harness for K bikes has a connector for heated grips. It is a "T" connector which has short leads and can be found under the tank on the left side about two thirds of the way back. It has two wires. The green/black wire is switched power from Fuse 1. The brown wire is a ground. Use the green/black wire as the positive input and the black wires from the old white connector as the positive output to the heated grips.

Symtec Heated Grips: (More info on Symtec grips here.) Get the positive input power from the OEM heated grips connector described in the prior paragraph.  This is a fused, switched power source. (Fuse 1) Use the white wires from the heating elements as the positive output from the PWM. Ground the red wires. (You could try running both the white and blue wires to the positive output but you may run the risk of getting too much heat and melting the plastic throttle tube.)

On my K1100RS I drilled a hole in the dash pad and installed the potentiometer and knob.

On my K1100LT I used a smaller PWM that I was able to build into the back of a switch blank. Since the bike is green, I used a green LED.

Having gotten spoiled by having variable heated grips on my K1100s, I decided my K75 needed them too. I built a hybrid of the two prior designs where I took the potentiometer from one of the PWM controllers at the top of the page and installed it in a BMW switch blank.  I had to cut down the sides of the switch blank a bit to get the potentiometer to fit.  When I was finished, I wrapped some electrical tape around it.

Since I planned to put it under the tank, I put the circuit board in a 2 3/4" x 1 5/8" x 7/8" project box that takes up much less room.

Here's the finished product, ready to be installed.

One of the nice parts of having an LED hooked up to the output near the knob is that it allows you to easily bench test it with a 12V battery before installing it. (If you bench test it make sure that the output wires that will attach to the heated are grips are not touching each other,)

My first two variable heated grip projects were on bikes that had BMW heated grips from the factory.  My K75 has Symtec heated grip elements. Each side has two heating elements, one for the high setting and one for the low setting. I hooked both elements up on each side to the output from the PWM so now I can get my grips as hot (or cool) as I want.

The BMW part number for a switch blank is 32711459318 - about $2.

By the way, if you're not into doing projects like this but still want variable heated grips then you can plop down $70 for a Heat-Troller from Warm-n-Safe to get variable heated grips.

Wiring diagrams:

© 2013 Drake Smith - Please do not use or reproduce this elsewhere.  Feel free to link to it though.