Peugeot 508 Rain Light Sensor

That sounds frustrating. I also own a 508 (not the hybrid) and had similar issues: erratic wipers, headlights, and dash dimming. It's almost certainly the rain-light sensor. Is your windshield original?

The windshield is original. What fixed it for you? Was it a sensor replacement, or more complex troubleshooting?

If it's the original windshield, I suspect it's the same issue I had. A workshop diagnosed bubbles forming under the gel pad where the sensor sits on the windshield. This interfered with the sensor's readings. They replaced the gel pad and recalibrated the sensor. I recommend you do the same.

Thanks for the insight! I'll get it checked out at the workshop, mentioning the gel pad issue. I've booked an appointment and they quoted me around 62€, so hopefully, that will solve it.