Um... hold fire for a bit. Later today (it's 04:00 here) I will drag my Switchboard, Charging, No.5 out of the shed and photograph both sides, plus draw out the wiring diagram and the switching "truth table" and measure the wiring.
It's not the same as your switchboard, but some of the basic wiring should be the same and you may be able to derive the connections for the missing terminals.
(I still think yours is an early Air Ministry version that bears little resemblance to the WS52 or WS19HP (Canadian) switchboard. Mine is intended for permanent installation in a Wireless Truck and I suspect there was a demountable switchboard issued with the "Truck & Ground Station" kit.)
Right now I need sleep.
Good Morning!
Chris (G8KGS)
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