Well, then lets look this thing over. According to the serial number, this is a first year production machine, 1963. If the switch was dropped from the model, other machines with the switch should have come before this one.
So .... was that a cost cutting thing, or did they add the switch later - or, were those switches added by the LSMG for the owners later?
My theory is that the switch was added later as the manual I downloaded from Singer shows the switch.
At any rate, this is the only machine I've got that does not have some form of switch for the light.
I do believe I may add one in the near future.