i agree with 30psi, it does look like the temp gauge wire, its located behind that rad pipe you can see in the pic
but whle that is unplugged does you dash temp gauge work??? coz if it does, then its not the temp gauge wire (obviously
) then it may just be a spare, as im sure i dont have any other spade connectors on mine in that area.
ill have a look on the spare head i have and take a pic if its still on there.
**EDIT**
