ALL WD bikes used the negative earthing system.........there was a point post-war that positive earth was used but didn't appear to last long......
I never use commercial "looms".......never correct and never fit.......I wire-up each bike individually and use period photos of the relevant year to get the fit and placement correct.........
Seemingly, wiring "looms" were never listed in WD parts lists..........only wiring "as required" is stated...........I would assume that at the various factories, electrical specialists would have wired-up WD bikes on the production line according to the particular year, contract and specification........and this varied..........take the earlier M20 for example, horn toward the rear rather than toward the front.......so, wiring configured on the production line according to fitments and contract.......