Lucas Prs8 anyone changed and upgraded to a more modern switch

Hi Paul,  I would just fit another knob with the proper bezel and 2 part securing device .i also fitted a piece of thin rubber to eliminate any looseness . Modern replacements are availiable, made in the far east. their durability has been questioned though. 

The Knob is secured with an expandable  2 part set screw  .

Green box's were used in the 1980s by a company with the name Lucas. The Red boxes have been re invented by a company known as Wassell who use the Lucas name but get the parts remade in the far East.
PRS8 there is no known direct replacement as after all this switch has 3 major functions when made in the early 50's 1)-to control alternator output for charging 6V batteries 2)-Switching the lights on 3)- Switching the coil ignition on. Uses 2 layers and 19 terminals-no problem. (service details on my web site)
Replacement-the first problem is the large D shaped hole in the head lamp, but the 850 Commando switch could go in the hole. But the depth of the switch with regarding the headlamp could be a problem.
Rewiring-yes the switch wires on the PRS8 are pushed in and screwed up, while the likes of the Commando have Luca terminals, the actual wiring/connection is easy (I can advise)

The two part screw invented by Lucas is I think a 4BA screw into the switch shaft, with a long shaft that secures the knob and another 4BA in the outside end that spreads the shaft into the knob, thus securing it. But in a lot of cases we find the smaller securing screw has rusted in-place hence it becomes unoperational. But several far eastern alternatives have done away with the adjustable part of the screw, hence it would appear that the 2 part is over and done with.
Further to the fitting of the switch it used to have a thin rubber washer between the switch and the inside of the headlamp, but you cannot use old innertube-too thick.