Working on the bench due to season.
View attachment 3179376
I'm working on a couple of things. First is making this a two-filament lamp. I'll get into that later.
Second is establishing an earth wire connection that doesn't need the hot green/yellow wire to pass thru it, like it came from the factory (white wire with black stripe is ground and lamp-socket spring seat).
Also, I don't wan't to sandwich a copper with zinc plating loop terminal under that monster lock washer. It would probably work, but, it is not going to look pretty after you take it apart after torquing it down, and I've never seen copper used by the OEMs for grounding on a vehicle, all their rings/lugs on the frame and engine are brass, and they ideally employ a star washer.
I once heard of using lead as body filler. A piece of 'bailing wire' was cleaned and 'tinned' with electrical solder. Then it gets a unshielded solid crimp connector, which is crimped, then soldered. The M14 nut will make the ground connection to the chassis of the lamp, and the lead coated soft steel wire should minimize corrosion at the location of thread/fastener. (I once had a plumber use a section of steel pipe for gas on an outdoor spigot, the galvanic reaction from dissimilar metals caused the valve to fail within six months, and the water was really discolored.) Hopefully the braided copper grounding wire and its connector stays dry with some shrink tube under the fender.
I'm not sure that this is really a trail going anywhere, yet...