The computer controls the relays for the fan. It does this by suppling a ground to the relay coil. Also you need to check and see if there is power on two of the wires. One of the four wires going to the fan relay has power all the time. This is the supply voltage for the fan. Another one will have power with the key on but not with the key off. Of the remaining two one goes to the fan to supply power and the other goes to the computer to supply ground for the relay coil when it is time for it to come on. Don't forget to check the ground at the fan motor connector too. I'll be around if you need me.
The wire that has power with key on will have to be checked with the engine cranking over. The ASI relay will turn off power to everything if there is no engine RPM in 2 or 3 seconds.