Mystery Grey Water pump switch

[keithw88]

Dear All,
Can someone identify my grey water tank automatic pump switch - photo attached? There is no maker's mark anywhere on it. It works, mostly, switching the pump on when the grey water gets high and switching it off when the tank is about empty. It's essential, but I have no idea who made it and whether I can get a direct replacement when I eventually need one
It is probably 20 years old, but not original to the boat (a 1976 Moody). The hexagonal head of the screw fitting is 50mm across the flats and the OD of the threaded section is 46.5mm. It functions on 24 volts.
Hope someone knows these things!
Keith