Whirlpool s20b rsb21 fridge not cooling

Freezer getting down to about -15 but fridge was up around ambient.
Internal and external fans running and condenser cleaned.
Build up of fluffy ice on evap, almost solid lump further down.
Continuity across defrost heater.
Continuity across brown/brown and orange orange of cut-out.
Could not detect continuity across white and blue of cut-out, and nor was there continuity between these and anything else (as far as I could tell).
There is also a black wire coming from the cut-out connector that plugs into the back wall. This wire is not connected to anything at the non plug end, and the copper is exposed as if the wire has broken off something. I thought that it might have broken off the cut-out, but when I look at this part on supplier’s websites it looks as if this is as it should be. Just seems strange to have an exposed wire dangling about like that.
Damper between fridge and freezer was open.
Is it a faulty cut-out or something more serious?

Any help very much appreciated.

Dez