If I had a Royal Enfield with no headlight switch (AHO) and I wanted to have the ability of switching it off, here's what I would do. I should mention this doesn't require cutting any of the motorcycles wires.
Loosen the headlight rim screw and take the headlight partially out.
Looking at the back of the headlight where the wires connect I would see three wires.
One blue, one green and one orange/amber or black.
The blue wire is the power for the high beam. The green wire is the power for the low beam. The orange or amber or black wire is the ground wire.
If the ground wire is disconnected, neither the high beam or the low beam will light.
Knowing this I would disconnect the ground wire.
Next, I would buy a simple single pole toggle switch. This is a "off/on" type switch with a lever sticking out of it much like the "light switch" found in homes but it is smaller with a threaded area just below the toggle and some threaded rings to hold the switch in a hole.
https://www.grainger.com/product/2X4...180409181605:s
To mount this switch if my RE had the "tiger eyes" type of casquette I would drill a 12mm hole thru the wall of it, probably just below the right tiger eye.
With this hole sized to fit the threaded feature on the switch, I could install the switch with the toggle lever sticking out of the casquette.
I would need some insulated wire and a couple of spade connectors like the ones that connect the wires to the back of the headlight. One male and one female connector would be required. The wire should be 10 or 12 guage size in order to carry the electrical load. (Don't use some thin speaker wire or it could cause a fire.)
http://www.repairconnector.com/categ...de-Connectors/
Cutting a short piece of wiring and installing a female spade connector I would install it on the headlight's ground terminal.
The other end of this wire would be attached to either of the poles on the toggle switch.
Another short piece of wire would have the male spade connector.
The bare end of this wire would be attached to the other toggle switch terminal and the male spade connector would plug into the orange/amber or black harness ground wire.
After the switch and the headlight were installed on the motorcycle I should now be able to have the headlight on at all times if the toggle switch was turned "on", or with the flick of the switch, the headlight would be turned off.
I should mention that when you are riding on the public roads, you should always have the headlight on (unless your trying to recharge the battery rapidly).
I should mention that if you can't find spade connectors, you could cut the orange/amber or black ground wire and connect the ends to the switch but this would usually require splicing in some wiring to reach the new toggle switch connectors.
If this is done, the splices should be wrapped with electrical tape to prevent unintentional grounding.
I also should mention that this change will also nullify the motorcycles warranty so don't do it to your motorcycle while the warranty is in effect.