Here are the pics I promised Peter, showing the firing 'pigtails' and some other useful details.
(Pics from IWM, British Official, Public Archive of Canada, and RAAF Official)
PIC 1. This shows the saddles which hang the RP on the rails, and the rails themselves. The RP's are 25lb SAP - note the slightly bulbous warhead.
PIC 2. The other type of rail used, and the different type of saddle, with the 'pigtails' hanging from the tails of 25lb SAP RP's.
PIC 3. These are AP rounds, note the slimmer head, compared to SAP. The pigtails are again hanging, and are only connected immediately before take off. Also visible here are the deflector plates between the rails and the wing surface.
PIC 4. Shows the 'pigtails' being connected, from the AP rounds, to the sockets set into the wing. The connecting wire, as far as I know, was a dull, brownish red colour, not unlike 'Winerot' panzer cammo colour, and the ceramic plug top was an off white, with a bright metal multi-pin plug. The shape of the deflector plate can be seen to advantage in this pic.
PIC 5. You've probably seen, or got this one, but just in case, that's your man in the centre!
Hope these help a bit, cheers,
T.