Radiator Fan
I just read your post today 10/11/08 I hope you will still get this. I have a late 1972 3.0cs with a/c. The factory auxiliary fan is a very poor design (no shroud the air is undirected). I wanted to improve the fan and connect it to an auxiliary fan switch also. I replaced the factory fan with a 13" Spal high performance fan, I found an unused temperature sender in the bottom of the front intake manifold. I think the sender might have been part of the emissions equipment, not all intakes have that fitting.
I used 2 relays one is fired by the a/c fan control the other by an auxiliary fan switch (92c) mounted in the intake. The fan switch I installed is used on most BMW's 1977 an later. It comes in a verity of temperature settings.
Doug