Hi,
Yes it's original, I re used it when I rebuilt the bike. You can see how it's mounted on the bridge plate in the previous post. As you can see the holes in the blade are not used, these are for when the switch is in tension eg rear brake on some bikes. On the D the switch is operated by the balance beam which moves up on that side of the bike when the brake is applied. You do the final positioning of the switch after adjusting the front brake. If you go the main site. Info,Technical,Components D, MO 110, you will see a small skectch of the switch numbered PR19/2. The Spares Co. hold these under part no.PR39/1 although there are probably other suppliers.
Mac