Himalayan - heated grips

Many years ago I had heated grips on my BMW.  They were very cosy. At the time money was very tight and commercial grips were out of the question. I put a 22Watt torpedo bulb inside each side of the handlebars, connected them to a switch wired through the ignition and Bob's your uncle. It worked fine.

I've changed the handlebars on the bike now and have installed Oxford heated grips.  They work well but the connecting cable are bulky, and get in the way.  The controller has the same issues.

I'm not changing them, but I'd like something a bit neater on the Himalayan so I think I'll go back to my original style.

It is very fiddly to mount bulbs securely inside handlebars, so this time I will go for power resistors.  These are cheap on ebay.

I do like the variable power on the Oxford grips.  It is done simply by switching the units of an on about once every two seconds. I don't intend to emulate that, but settings of 100% and 50% will probably be OK.

The Circuit.

This is very simple. One resistor dissipating about 24 Watts (at 14V) in each side, and another resistor which is switched in series with it to reduce the power to about half.
A little more than half for the RH side to allow for the extra insulation imposed by the twist grip.. in series with it to reduce the power to about half.

The Switch. 

One wire has to come from the ignition circuit, ideally through a fuse. Two have to go through a hole in the handlebars from the switch.  Another wire has to go into the handlebars for the 0V line as I'd rather not risk sending the current through the steering head bearings. An electric bike controller looks like it would do the job. Single Pole, Double Throw, centre off.  It's cheap, but maybe a retro indicator switch would look better. Maybe fitted between the handlebar brackets with the hole in the bars covered by the switch.  Use the exit wire hole in the switch to bring in the power connections (3.5A so use 10A cable) 

 The Heaters. 

Obviously these will get quite hot. The only way they can lose heat is into the handlebars.  Power resistors which can operate up to 200C should be fine. Soldered connections melts at 188C. High temperature cable inside the bars further insulated where they pass the resistors. The handlebars are 19mm inside diameter and it looks like the 8ohm 100W power resistor I bought as a load for another project will fit after grinding of the food I really don't know how hot they will need to get to keep my hands toasty when the heat has to go through the bars, twist grip, grips, and fairly thick gloves. A good thermal connection to the bars would be ideal.  Maybe with wire wool packed around the resistors? How to keep the wool in place and stop it touching leads?

Update 05/03/20 Now I have the Himalayan I can look at it properly.  It looks like the inner of the bar end weights are welded in. I can't get in there. So this mod would require new handlebars. Oh well, a good theoretical exercise. Maybe it will come to fruit if I ever change the handlebars.