The fan on the outside of the radiator and intercooler will not shut off. It has done this before and run down the battery and did not come back on after having the car jumped. Tonight it ran down the battery on my wife, she had it jumped and drove the car home, when she got home she told me what had happened and the fan was still on. I unplugged it so it won't run down the battery again, but how can I solve this problem for good. The car is a 1990 740ti. Thanks in advance for any help.

There is a relay type of thing that is clipped to the coolant resivoir, I took this off, unplugged the plug that goes into it and the fan stopped running. It did not stop when I pulled the wires to the temp. sending unit in the radiatior or intercooler, I don't remember which it was in. I suppose this means that this plug (temp. sending unit) is bad. Could the thing (i don't know what it is) clipped onto the coolant resivoir be bad also, and what is it called if any of y'all know. Thanks for the help.

I had to replace the switch / sensor in my 745T to correct this problem - at the top of the radiator. I wonder if the plug you've pulled isn't the one that goes to this switch?

I unplugged the power connection directly to the fan. I found the plug you are speaking of and unplugging the wires did nothing. Thanks for the reply

Check the relay on the coolant tank or the temperature sensor in the radiator. Either of those could be stuck closed, keeping the fan running nonstop.
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The relay has battery power to the main contacts all the time so if the contacts weld together from heat the fan will continue to run after the key is turned off,replace the relay.

Where is the relay?

The fan relay on my 90'b234 motor is on the r/s strut tower,next to the injector power relay(RFI)they are the same relay,try unplugging the one closest to the fender while you fan is on to see if the fan shuts off,if the motor dies then unplug the other.By the way,that fuel injector relay can cause strange starting problems; so keep that in mind for later.