Garage Cabinets, Garage Storage, and Garage Organization

Hi everyone.
Just got my first BMW - a 1999 Vreg 523i SE in black and absolutely loving it. After two Golfs (a 1.6 petrol and a 90bhp diesel) this is a beast, but a beautiful beast. It has one issue tho. After polishing it the other day, i had the bonnet open and discovered that a plug had been disconnected. I didn't fancy plugging it in as it had obviously been recently disconnected (as the contacts were still very clean and shiny) for a reason. It is located (as you stand at the front of the car looking at the engine) to the right of the o/s headlight. Could it be for the cooling fan? Any suggestions on this matter would be very gratefully received.
Wondering how after 10 years of driving i settled for less than a BMW. They're awesome!!!
Cheers
Chris