According to schematic for your car Keith there should be a red/green cable from slow speed relay that routes through the Ford resistor and on to fan motor. The red/orange cable you mention is common feed to fan motor connector after junction of the two relays output (slow via resistor). Another clue to its existence will be a bank of six identical relays - starter, fuel pump, ECU, fan low, fan high, air con. The car is wired for air con if fitted or not.
