I am not sure if I am using 20 or 22 gauge wire, but I am pretty sure it is one or the other. I live in USA, I do not know if our wire gauges correlate to wire sizes in your country. It is insulated, I wrapped two pieces together and zip tied it to my fork. The wire I am talking about is the yellow wire in the photo.
I bought some 2.8mm spade type connectors and use those to connect or disconnect the wires to things like lights, etc.
My taillights are battery powered, so I only have wire along the fork leg to the headlamp or if I am touring to a separate USB charger that runs in parallel with my headlamp.