Doug/Mogdriver, many thanks for taking the time to reply to my request for further info. Coincedance or what, I found a wiring diagram drawn to depict operation exactly as you initially described on in this thread as per GoMoG.
I found a diagram in the Haynes manual for the Rover 3500 V8 No 356 of the Haynes manual series. There is also a drawing of the oil pressure switch connections on page 131 and wiring diagram on page 140 of the same manual, though the diagram also contains a lot of kit not fitted to a Morgan.
Beamed up the GoMoG site and used your directions to find the appropriate page http://www.gomog.com/allmorgan/Plus8isolatorswitch.html
Early hours of the morning here, thus not dressed for the cold garage..(-: Seems that my issue may be that my oil pressure switch is not fully functioning internally as it should. While it does provide voltage to the pump when the ign switch is in the RUN position, engine running, oil pressure is present, by closing two of the contacts on the three contact pressure switch, and thus disconnects the same voltage when there is no oil pressure present.
My issue would seem to be that the third contact which should supply voltage to the fuel pump when the ign key is held in the START position does not do so.
The three connection oil pressure switch would seem to be configured to have two of it`s contacts connected internally when there is no oil pressure....and in that situation the white and brown wire will be connected to white and purple wire through the switch.... Thus when the ign key is held in the START position the white and brown wire becomes live, supplying voltage to the switch and thus passing voltage on to the white and purple wire causing the pump to run and fill the carb float chambers with fuel.
Once the engine starts and the oil pressure builds the internal switching action of the oil pressure switch breaks the connection from the white and brown to white and purple, and simultaneously makes a connection from the white wire to the white and purple wire that is connected to the pump, thus the pump continues to run providing the carb(s) with fuel for as long as there is oil pressure present as detected by the switch.. thus all is running normally.
Should there be some sort of accident where the ign is left on but the engine stalled there will be no oil pressure thus the fuel pump will stop operating.
I noted the by-pass suggestion on GoMoG Doug, I had contemplated something along similar lines using the starter button switch I had in my kit that once graces an old S Type Jag...(-: Though some years back had wired in "temporary" by-pass to achieve the same aim, having picked up voltage from the rear sidelight near the pump passing that through an unmounted switch from the switch to the pump, providing a temporary supply when the sidelights were switched on and the temporary switch ON.... Thus for the by-pass to operate two switching actions had to be performed, side light switch had to be on and the temporary by-pass too...which could be done prior to engaging the starting process if required... I had planned to use the starter button in place of the temporary switch, to add a degree of safety should the button be held on in an accident situation, but how far does it seem reasonable to take this stuff....I think your idea of manually filling your Weber carb float bowl works fine.... Not so easy on Strombergs or SUs though.. (-:
Of course there is a balance to consider... IF the three connection oil pressure switch is operating normally then the battery may well have enough power to fill the carbs while the starter is spinning the engine though after a lengthy lay up perhaps less so..at which time the by-pass circuit may seem a reasonable idea may be fire up the engine pre filling the carbs should provide a quicker fire up of the engine, which may not be ideal as the oil will perhaps not have time to begin to build pressure.. thus allowing the engine to turn over without firing up for at least a few revs, before activating the by-pass or manually topping up a Weber may seem reasonable...?
More than happy to read alternative thinking, and thanks again Doug.