The Megane 2 was probably the worst car Renault made. The electrics are laughable.
The window regulators are a major pain. As snapdragon69 said above, the black box of electrics is the culprit, but you can't buy them separably. Renault know about this issue, and a dealer will replace any faulty regulator for £100 I believe it is, as long as it's within 10 years old and 100K miles.
Water ingress is another problem. Usually from blocked water drains of the scuttle panel, but have also seen water come in from the front door panels.
This usually collects under the carpet and saturates the sound deadening foam. There is a large electrical connector joining the 2 main looms together on the N/S. The water corrodes the wires which eventually break.
The Delphi diesel system fitted to the 1.5dci is a joke. Seen so many scrapped due to the high pressure pump breaking up and blocking the injectors up. Last time we priced one up, I think it was about £1k plus labour.
Key cards are a nightmare. Renault are starting to lock down their new cards now, so have to be ordered on VIN number which take up to 5 days. Always keep a spare one!
I work for a Renault independent
