Auto dimming wing mirror no longer dimming

[ab1702]

As above really, it no longer dims but the mirror still moves with the control on the door knob.
Is it normally just the glass that’s at fault or could it be the cables in the door? Everything else works fine.
I also know how expensive the glass is to buy but I found a brand new one on eBay for £45 which I bought a while ago but I haven’t got round to swapping it yet and I’m working away at the moment.

 

[NHN]

Check the door hinge rubber for broken wires, often the case, to prove if it's the glass swap sides temp & retest.