Just checked through the wiring diagrams. Just as Rick89GTS said, the fans are wired to run constant if any sensor fails.
The radiator fan relay is normally closed, giving the fans power all the time. The relay's trigger wire (which turns the fans off) is a system ground - which goes through the A/C pressure switch, then a check connector, and then through the water temp switch to ground. This wire is blue / black according to my BGB.
Do you have a digital multimeter to test for voltage and continuity?
So, testing the system from the end of the circuit up:
1. water temp switch - as stated eariler, connect the blue wire to ground or bridge the 2 wires together. Jumping the blue wire to ground is a better option, since bridging the wires assumes that the white wire has a good ground connection. You can check the ground by testing for continuity between the white wire and the negative terminal. You can also check the blue wire for voltage - no voltage means something is dead before this sensor.
2. Check connector. Make sure its connected - See if the blue wire has voltage here. If there is no voltage, then continue on. If you do see a voltage, then make sure the wire is getting to the water temp switch (continuity test). You can also bypass the temp sensor and some wiring here and connect the blue wire to ground.
3. A/C pressure switch. Check for voltage here, or bypass it and connect the blue wire to ground taking the check connector and temp sensor out of the circuit.
4. Radiator fan relay. If everything above has passed, then it could be a bad relay. Just like before, you can bypass the whole circuit by connecting the blue wire at the relay to ground. This should cause the relay to "click" and the power to the fans should stop.
Have fun!