Seat Altea Lighting Issue

Sounds like a dodgy connection alright. Are your tail lights acting up too? Sometimes a bad headlight switch can affect more than just the headlights. Have you checked the dimmer switch for the dashboard lights? Wiggle the car switch around a bit, see if that makes a difference. Could just be a loose connection.

Tail lights seem fine, and the dimmer switch seems to be working as it should. When you say wiggle the car switch, do you mean the headlight switch itself?

Yeah, I meant the headlight switch specifically. If the tail lights and dimmer switch are behaving normally, and you're still getting random headlight activation and a stored fault, it's pointing pretty strongly towards a wiring or the switch itself. Could be a pain to diagnose fully. Might be worth getting a workshop to take a look before you start ripping things apart. They have the tools to pinpoint the fault quickly.

Thanks for the input. Took it to the workshop, and you were spot on. They found a defective cable or plug connection with the light switch. Cost me 95€ to get it sorted.