I purchased a length of cable and translucent heat shrink from ** Please log in to view ** Stripped the cable, fed through the heat shrink and warmed the heat shrink to form a translucent length of cable.    

sunny said
hi  Alan   i  use      tined   copper   earth  wier  [  green  & yelow ]  from  thins like a  kettle    chep   &  it  has  to have  about  the same in  copper  wier inside  

This ^^^ isn’t a great idea. Automotive flex is normally 14 strands of 0.030” cable for an 8.75 amp load (at 12v), in a sheath designed for the environment. Domestic flex is designed to take lower current at higher voltages, has more strands of thinner copper, which is less resistant to vibration, and comes in a flex intended for an interior environment. 

The reason translucent flex isn’t available any more, and it’s been near impossible to get for the forty odd years I’ve been playing with Bantams, is because the material that it’s made of isn’t durable enough. 

You’re a grownup. Make your own decision whether visual accuracy, on something near impossible to see, that most people wouldn’t even notice, and those that would will understand exactly why the compromise was made, is more important than safety/reliability. 

Anyone that points to a bit of wire on your bike, at some point down the line, and says “ooo, that should be translucent” is not someone you should be paying any attention to. 

The earth cable for the rear light will be no more visible than the other two wires for the rear light

It will look deliberate and "belong", mine does (to me – I'm assuming you're running all 3 tail light wires together?)

As far as I know, and can remember of my D3, the common earth point on the frame is the top toolbox mounting lug under the top frame tube, or even the rear tank bolt lug. I am going to use the former.

Note you need to remove all paint from it, where the earth tag will go, to get a good electrical connection.