I've got a 1.6 HDI dispatch, roughly 2010 in year. Here's some of the general 'might need to know' bits:
- Battery is a bit weak, at 12.3v ish. Has started, unlocked etc fine but is almost always in eco mode
- Everything generally works - no other issues I know of
- No water ingress triggers
- My lexia chose a good time to start playing up, but generic OBD2 reader showed no P codes
Went to start it up after I'd turned it off and removed the 12v feed to the rear camera, and turning the key had it beeping through all the possible faults (brake failure, airbag failure etc), and the dipped beam symbol is lit up - but the dipped lights won't actually come on. Tail lights seem to come on with ignition and won't go off, and it doesn't crank - you can hear a relay click but that's it. Dash looks like this:

I have tried all the usual candidates - I'm 99.9% sure that the jobby I was doing was unrelated, and I didn't do anything stupid/accidental in the 12v wiring - it seems just coincidental. I did try some brief BSI resets, but achieved nothing. Disconnected the rear lights and door looms just in case there was a short.
I've ordered a new battery just in case it's anything weird like that, but I'm stumped otherwise.
Is this a weird "having a tantrum" PSA thing that will - hopefully - either resolve itself overnight, or with the battery disconnected for a while - or even with a new battery?