So, EPC light came on and brake lights stopped working, so I replaced the brake light switch according to the guides I found on this forum. Brilliant.

 

Part of fixing it involved removing the panel with the headlight off/sidelight/main beams selector, headlight height adjuster and dashboard light intensity thing.

 

Previously, a buzzer would sound if I left the lights on and opened the door, then stop once I'd turned the lights off (or closed the door).

 

Now, the buzzer will sound if I leave the lights on and then open the door. And carry on sounding until I close the door or put the key back in the ignition and turn it one click.

 

And if I turn the lights off and close the door, the sidelights on the LHS of the car (parking lights?) are on. I don't know if they'll go off with time. This is new!

 

And then when I open the door again, the buzzer beeps again.......

 

 

So, what have I broken and which wire do I cut to fix it?!

Check that you haven't accidentally knocked the indicator stalk downward, as if you were indicating left. This will cause the parking light behaviour and maybe the other differences you're seeing/hearing.

I think you called it right because I went for a drive and it's fixed itself