Early WD Norton Big4 sidecars appear to have been fitted with the long Lucas sidelight similar to the MT1130 tail lamp fitted to BSAs in 1940.
Later WD Norton Big4s used the Lucas RC330.
This is from the Big4 maintenance manual 101/NC2
This from Big4 contract C7576. List of proprietary equipment.
And from Lucas maintenance instructions for motor cycles supplied to H.M.Forces.
email (option): robmiller11@yahoo.co.uk
Here are the two I bought at Beaulieu, both are brass bodied, one has the Lucas seal the other doesn't, but which is correct for a 1941 Norton Big4?
email (option): robmiller11@yahoo.co.uk
Rob I have seen these identacle lamps by different makers. I have seen them with the WIPAC medalion and another make that I can't remember. Also without a logo like your black one. Since Norton used LUCAS. That is what I used. Ron
email (option): ronpier@talk21.com
Rob, even my pictures don't enlarge that much! here's one that shows that a medallion was used, and since P&H was taken over by Lucas in the late 30's it will probably have been a Lucas one, but nothing's certain!
Have other pictures that seem to show nothing on top of the lamp.
Ron, never seen one with a Wipac make though?? did that already exist back then??
Then there's the thing that occured to me, Always thought that the rib on the mudguard went with the early Lucas lamp, but it did not! only a little later, have to pin it down to a contract one of these days!!
Saw a pair of these (P&H) lamps for sale at Beaulieu, but for 180 pounds a set, I left them for someone more fortunate 
Cheers,
Lex
email (option): welbike@welbike.net
Well I could be mistaken about the Wipac thing? I have had four of those lamps during the last few years. Two had medalions from other makers, one was plain and the other was from the Prince of darkness himself
Ron
email (option): ronpier@talk21.com