I've just replaced the RH DLR/Sidelight bulb. The DLR filament had blown. i bought two because I reckon that if one side has gone, the other won't be far behind.

My question:
I've looked at the Haynes book, the car handbook, and at the guide on here about bulb replacement, but when I take the rectangular cover off and the circular rubber cover under the front wheelarch, I see a total of three fittings.

The DLR/Sidelight, and the Full Beam bulbs are inside the circular rubber cover of course, but what is the bottom one below the circular rubber cover?
It's green and has some wires coming in/out of it and I see no info about it.

The Dipped Beam and the Indicator are under the bonnet of course and the Fog Lights are in the front vallance, so I can't for the life of me figure out what this third thing is inside the wheelarch cover.

Thanks,
Mick.

Any ideas?

Rectangular cover removed under the front wheelarch front.
Large circular cover over the main beam and sidelight/DLR bulbs.
Directly below the large circular cover is a green connector that looks like a bulb holder with wires attached.

What is it?

Regards,
Mick.

Haynes doesn't immediately show anything obvious.

My thoughts would be horn (it isn't) or temperature sensor- haynes mentions a coolant fan temperature sensor for models with A/C (NOT the coolant temperature sensor or exterior temperature display) but I'd be screwed if I could think why FIAT would put it on the bumper or something to do with the SRS.