Cooling fan wiring

[andy b]

Hello,
I need to return my cooling fan wiring to the original layout (I had it operating manually with a switch on the dashboard). I have the wiring diagram for my car, but my electrical knowledge is so pathetic that I can't figure out the wiring of the relay. According to the diagram, the circuit should be wired as follows:
Fan motor +ve (red) is wired direct to the battery +ve terminal via an in-line fuse.
Fan motor -ve (blue) is connected to the relay.
A 2-wire thermo switch on the radiator has one wire (black) going to ground, and one wire (white/black) to the relay.
The other two connections to the relay are:
a black/red wire which goes to the fuse box via another relay (live with ignition), and
a blue wire going to ground.

Usually, if an accessory (e.g. fog lights) is wired via a relay, when the relay is triggered (e.g. by a switch on the dashboard), a +ve wire from the battery is temporarily connected to the +ve side of the accessory. As I understand it, my fan circuit does the same thing, except that instead of connecting the fan motor +ve to the battery +ve, the thermo switch causes the relay to connect the fan -ve to ground. The result is the same, since the fan motor circuit is then completed. Hope this makes sense so far...

So, if you have a normal 4-pole relay, with terminals marked 30, 85, 86 and 87, how do you connect it? So far I have succeeded in getting the fan to switch on when the correct temperature is reached, but once it is running it will stay on until I cut the ignition, even when the engine has cooled sufficiently. If I start the engine from cold again, the fan is off until the temperature rises again, so the thermo switch does seem to reset itself. What am I doing wrong here?
Any help would be much appreciated. Oh, and the car is a 1974 coupe with the 1800cc engine.
Regards,
Andy