Are you using OEM BMW grips or aftermarket?

Either way there is (should be) an open plug in your wiring harness for grips/accessory. It is (should be) fused already (one of 4 in your fuse box).

Imagine you could tap into the open line/harness for power, if aftermarket. 

No real need for a relay---though that is your call.

I've had heated grips (OEM) on bikes of that era (Mystic, GSPD) and other airheads, never a relay. Just fused. 

Here are some pics of what the plugs/harness looks like, via MAX BMW. Check diagram #32 (Steering)

https://shop.maxbmw.com/fiche/DiagramsMain.aspx?vid=51635&rnd=09082020

Good luck

With apologies from the start, this "plan" (as presented) is a VERY bad one. First of all, when your grip switch is ON, your grips are ON and consuming power. It will happen repeatedly that you jump off your bike to join a group of riding friends for lunch and come back to find your electric-start-only bike with a dead battery. This will not only make you mad as all get out, but will put off your riding buddies to the point they no longer wish to ride with you. I know this because I have lots of "buddies" I have crossed off my "ride with" list because their accessories are wired this way. It's a needless and senseless PIA for everyone.

What I would suggest is....

1. Install an LED headlamp bulb. That will allow enough current capacity in your headlamp circuit to safely power the grip heater through the Gray headlamp circuit on the rear of your ignition switch. In this way when you turn OFF your ignition (as you surely will), your grip heaters will also turn OFF.

2. You also did not mention the magic word "Fuse", but you did say you had no wiring diagram. That's a VERY bad combination, and so the possibility of smoking your main harness is VERY real. Not only are new harnesses VERY expensive, Mr Murphy predicts you will be at least 200 miles from home when the event occurs. May I suggest you connect to the rear of the ignition switch (at the aforementioned Gray wire) with a weather-proof flat pack fuse holder and install a 4A fuse. This will provide the missing electrical protection that is required.

The fuse holder will supply power to the Grip Switch. The switch will supply power to both grips in "parallel". The "Return" will be made by connecting to the Brown section of the multi-color wiring board (lower RH corner) inside the headlamp shell. All this wiring is using 16AWG multi-strand automotive wire with 'heat shrink' on all soldered connections. 

This should make everything safe and easy... and a lot more fun for you and your riding buddies.

Hope this helps.

I will add some needed detail.

I bought Bikemaster heated grips. The quality of the materials is high. The controller incorporates a voltmeter.  The wires to connect to the battery are fused.  They are reasonably priced. They are impressive in the flesh and enjoy positive online reviews.

I prefer to power them directly from the bike's battery. By incorporating a relay, the danger of draining the battery is eliminated. A relay is simply a switch that allows the heated grip circuit to function only when the bike ignition is turned on. 

The question I had/have is simple.  What switched power wire should I use to drive the relay?  From what I've seen in the comments, the answer would be the gray wire at the ignition switch, which is to be connected to either relay post 85 or 86. A frame ground or a brown wire in the OEM loom would then supply the ground. 

Thank you for your help!

With the after market grips/voltmeter/display combo, you've got a bit more going on there than just a traditional OEM set of heated grips. That bit if detail was/is important. 

I can see your wanting to add the relay with these and your wiring plan seems fine. Adding a fuse or fuse block-even better. 

Anecdotally speaking, I've seen 20+ years of OEM heated grip using the simple fused circuit on a number of airheads---never a dead battery or fried harness.

Hoping we'll cross paths for a ride one day, Mr. Whatley, that would be fun! Make sure you reach out if you are ever in the Ozarks.

Cheers fellas!

I see your kit already has in line fuse, so even better. 

Good luck, let us know how it goes. 

Congrats on the new bike, too. I've enjoyed the R100R models I've owned, hope to have another one someday. 

Please keep us updated with some pics as well, kinda quiet around here.

Posted by: @632

I will add some needed detail.

Thank you. You asked for help, but then gave few details.

I prefer to power them directly from the bike's battery. By incorporating a relay, the danger of draining the battery is eliminated. A relay is simply a switch that allows the heated grip circuit to function only when the bike ignition is turned on. 

Forgive me, but "the devil is in the details".

• If your system includes a relay, the the grips are not connected to the battery. Thanks for the clarification.

• Since the gray wire is not electrically protected, you may need 2 fuses: 1 for the relay and 1 for the grips.

The question I had/have is simple.  What switched power wire should I use to drive the relay?  From what I've seen in the comments, the answer would be the gray wire at the ignition switch, which is to be connected to either relay post 85 or 86. A frame ground or a brown wire in the OEM loom would then supply the ground. 

• The Gray wire at the rear of the ignition switch to power the relay, IF you add an LED headlamp. Again, "the devil is in the details".

• Use one of the open terminals in the RED section of the multi-color circuit board to power the grips.

This will keep all your wiring simplified and concentrated at the front of the bike.

Hope this helps.

This is the machine on which the heated grips will be installed. It has a Parabellum Scout fairing, the windscreen of which appears oddly tall in the photo.  In reality, it is not so. 

Nice bike !