that was my thought exactly, need to trace it back and see.
also i think fred asked if it had a conversion done, becasue spare wires are always a problem with conversions
2 other things
1) you said the oil light comes on normally at start, i am assuming it goes out shortly after starting .... this would indicate that it is not the oil switch
2) i assume you meant you were having trouble now we are into freezing weather .... this can be a number of things
that connector looks like it should push on to a round turret connector, but those usually have 2 metal pieces in them or possibly a ring one to allow it to hold in place, this could be why its come off
once you have tried tracing it, stick a multi meter on it, lets see what you get on that line and when
