That's what I wrote but consider if something should go wrong with it and blows the fuse you will probably lose all the lights on your bike and maybe other critical things.

It would be much safer to put the charger on its own fused supply.

 

We ( in Belgium ) have the same headlights as in the UK, I always have used the power from the headlight to power a aftermarket USB socket. They draw very little power
from the system and never ever had any problem with it ( guess I install about more then 20 pcs now ). The reason why we take the power there it's because it is easy and
contact switched.

 

I have also taken power from the position lamp wire for my sat nav. I just wanted to point out to someone who may not be aware of all the angles of what might happen.

 

The position lamp wiring is protected by the 15 amp P&A fuse. I've never seen a USB charging port that pulled more than 5 amps. Most of the single port units pull 2 to 3 amps. Done correctly, the OP should be fine.

 

I am not disputing the cable or bike fuse should be able to handle a USB socket.

It is a point of view I am making people aware of so they can make an informed decision as to whether or not to use the position lamp wiring to power an accessory.

The potential risk is the fuse blowing and then an unknown amount of items will also lose power.