This is not an original idea, and forgive me if it's been covered elsewhere, but as these bikes get older aging accessories are more likely to cause issues with the electrical system. The root issue is that while BMW fused the lights and turn signals, they provided no protection for items connected directly to the battery. As I recently found out, one small fault can toast the entire electrical harness.

My issue was associated with the dashboard clock which shorted out. This melted the insulation off the feed (Red) and return (Brown) wires in the main and the dashboard harnesses, and actually started a fire under the dash of my RS !! This was really scary. Total cost of the 2 harnesses was $360.

MAIN HARNESS
The loss of a harness is entirely preventable with the addition of a small fuse holder. The issue is that any items connected to the Red wire on your Airhead are directly connected to the battery all the time. What I suggest is that you purchase a common "flat pack" in-line fuse holder for an ATM size fuse. Crimp a male spade lug to one lead, a female lug to the other, and fit a 20A fuse to the holder. Such a device is shown below....

ATM in-line fuse holder

To install, simply unplug the Red wire from the rear of the ignition switch. Plug the female connector on the Red wire to the male connector of the fuse holder. Then plug the female connector on the fuse holder to the #30 terminal on the ignition switch, the position just vacated by the Red wire. In this way you can increase your harness protection, without having to modify the harness itself.

CLOCK
If you have an RS or RT with a dashboard clock, then you'll need to make up a second fuse holder. This fuse holder will be identical to the first, except that the value of the fuse will be much lower at 2A. Installation is similar too, except that the action is taken with the Red wire on the rear of the clock.

This is not 100% protection, the only way to do that is modify the harness, which would require knowledge of soldering and using heat shrink tubing. That may be beyond the capability of most owners. However the method presented affords 99% protection with no permanent changes to the motorcycle at a cost of about $4. And too, it can be completed "on the bench", then offered to the motorcycle. I judge that to be adequate protection, at an acceptable cost and level of difficulty to fit most Airhead owners.

Hope this helps.

PS. Also see this thread.... https://www.airheads.org/kunena/wrenching/392-home-mechanic-more-reliable-fuses#2849