Can anyone help me with this? For some reason I decided to check the air filter on my series 4. I noticed a white wire (in a "sleeve") with a female spade connector just hanging below the filter housing in the general zipcode of the alternator. The wire runs up to the main harness and appears to go through the firewall (I am guessing to the fuse panel). Anyone have a guess what it might be? I have not found any part of the electrical system not working - but something might have not been working so long that I don't recognize it. I have only spent 8-10 hours trying to track this down so it is early days. Since I have owned the car since about 1993 (it's a 1991) I don't think I can blame a PO and it does appear to be part of the original harness. I have tried to trace using Papajam's drawing - but I am over my head here...attached is a photo with a paper towel background so that you can see the connector.