Just come accross this after searching for the lucas dimdip. Would seem to be a landrover defender part. Says it all really and Ive just spent two days pulling every light out of my car. Time to unplug and forget. It's the Dim-Dip Transformer, it's probably been un-plugged because it's failed. When they fail - Dipped Beam comes on and stays on, even with the master lighting switch in the off position. The Transformer costs a small fortune to replace and, as Dim-Dip is no longer a requirement, I would leave it un-plugged. PRC6336 - Dim-Dip Transformer for Sealed-Beam Headlamps - £149.39 inc VAT