Ok so I didn’t think I was thick but clearly I am. Just put led bulbs in the rear lights but cannot fathom out how to get the red clip to snap into the locked position. It was difficult getting it off so I unclipped the bulb holder assembly from the lense I can see how it’s suposed t work but can’t figure out how it clips back on to the loom to lock it in place. Suggestions to an obvious numpty please. (2019 sel green tech 75) 

Would be happy to think about this with you, but I have not yet had to change a bulb on mine - I am wondering if it is possible that there is a fit/interference issue with the new bulb.... How about a photo show us what you mean?

Clearance on the bulb is fine, it’s simply the red clip that holds the plug into the lamp housing 

Old topic...

 

But I recently got to changing  the reversing light bulbs to LEDs, and I see what the "red tab" is all about now !

I found it very hard to pull the red tab out to disconnect the wiring connector, but easy to push back in place after changing bulbs (exact same car) after the connector mates in the body of the bulb holder.

To pull the tab out, I ended up fashioning a kind of 90 degree "crochet hook" from an old bradawl , so the point of it went under the red tab in order to lever it out. The design of the locking tab is basically stupid!