The main connector on the right hand side of the dash.
I don't know how to lift the red thing to add a new pin.
I've tried using a small screwdriver, but I'm in danger of damaging it.
Is there a place that releases it?

 

Normally those inserts are released from the backside of the connector and that red part slides forward. I have to get a strong light and some magnification to see what to do as they all seem to be different.

Can you see anything that looks like red plastic when looking on the backside?
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Thanks I managed it. I couldn't see anything to release it
So I used to tiny screwdrivers either end and just pushed it up. It moves about 8mm.
Then discovered my loom for the illuminated tread plates is different to the one in the really helpful write up on here.
But all sorted now.

 

Great to hear!
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They work!