Peugeot 307 Lighting Fault

Sounds frustrating! I had similar electrical gremlins in my old Focus. First, check the bulb holders for corrosion, that can cause weird issues. Failing that, the light switch or the wiring harness to it is a good shout. Is it all the lights or just certain ones? Have you tried wiggling the switch to see if that makes the fault appear or disappear?

It seems to be all the lights that are affected, not just specific ones. I tried wiggling the light switch like you suggested, but it didn't seem to make any difference. Where exactly would you suggest I start looking at the wiring harness?

Okay, since it's all the lights, and wiggling the switch didn't do anything, I'm leaning towards a more widespread issue. The wiring harness for the lights usually runs along the steering column. Honestly, chasing electrical faults can be a nightmare. Given the error code and the symptoms, it really does sound like the cable or plug connection is defective. I hate to say it, but for something like this, it might be worth taking it to a workshop. They've got the proper diagnostic tools and experience to pinpoint the exact problem.

I was hoping it'd be a simple fix, but it looks like it's beyond my skillset. I took it to a local mechanic, and you were right – the cable/plug connection was faulty. They fixed it for 95€.