in my 240d, i have a disconnected wire that looks like it should plug into the battery (has a battery lead). It is a small red wire that is resting by the battery (not connected) and it goes into the firewall on the passengers side on the edge on the left side of the battery. What does this one red wire do? It looks like it has a ring as in one end should attach to the battery's positive connector, but is just hanging there?

Something to do with A/C, clock, cruise control? I can't seem to figure it out.

Thanks!

(240d manual 1982)