Thank you Nin for making me get up off my lazy arse
Sooooooo...........
Light Switch ~
Old switch has 13 wires at the switch (2 x black/blue) & 13 wires out to the connector block (2 x black/blue go into one pin).
New switch has 13 wires at the switch (2 x balck/blue) & 12 wires out to the connector block (1 x black/blue goes into one pin).
The above threw me initially but I can only assume the 2 x black/blue wires are spliced together somewhere in the short switch loom (I wasn't gonna unwrap it to find out).
My issue with things not doing what they should was down to the green & green/black wires being swapped in the new switch V the old one. Once I swapped those over in the connector block all was good.
Diagrams below show old V new switch wiring and where I've written 'top' & 'bottom' that refers to how the switches present themselves to you when held open like this
<a href="https://andressotoscastello.smugmug.com/UkGSer/n-5CFLKf/i-W3HZS7B/A"><img src="https://photos.smugmug.com/photos/i-W3HZS7B/0/b952e485/XL/i-W3HZS7B-XL.jpg" alt=""></a>
Here's the layout of wires; old V new. You can see the green & green/black swapped over
<a href="https://andressotoscastello.smugmug.com/UkGSer/n-5CFLKf/i-dvJ3vhL/A"><img src="https://photos.smugmug.com/photos/i-dvJ3vhL/0/f48218f8/XL/i-dvJ3vhL-XL.jpg" alt=""></a>
When looked at head on like this
<a href="https://andressotoscastello.smugmug.com/UkGSer/n-5CFLKf/i-ScL38zH/A"><img src="https://photos.smugmug.com/photos/i-ScL38zH/0/a9083247/XL/i-ScL38zH-XL.jpg" alt=""></a>
The 'correct' wiring should be as follows
<a href="https://andressotoscastello.smugmug.com/UkGSer/n-5CFLKf/i-xrSGTF5/A"><img src="https://photos.smugmug.com/photos/i-xrSGTF5/0/2e451e13/XL/i-xrSGTF5-XL.jpg" alt=""></a>
Of course, that all assumes my main loom and yours are the same
HTH
Andres