Since his car is overheating because of the fan not coming on as it should, I would have first suggested the coolant switch. Now that you have replaced that to rule it out, you need to make sure that coolant is actually touching it. That sensor does what it's supposed to based off of coolant temperature, and if there isn't enough coolant in the system to even make it to the sensor, then it won't work right. That, or if the system hasn't been bled properly and there is too much air in there. Another possibility is the system has a pressure leak somewhere, and is not coming up to the proper psi. If the thermostat is crappy, it won't let the system pressurize. Touch all of the hoses after the car is warmed up. Are the upper and lower radiator hoses, and both heater core hoses warm? Is the upper radiator hose rock hard when it is running? Does the system pressurize when it's running, and does it hold the pressure for an hour after the car has been shut off? I wouldn't jump to rigging up the fan to the fuse box just yet, if this is going to be your daily driver. It's hot as crap out there right now, and you definitely want your cooling system to be in tip top shape, if you need this car to run reliably.
*EDIT*
The sensor you replaced had two wires, right? I know the two sensors are near eachother right by the EGR; this one should have been the lower one.
*EDIT*
The sensor you replaced had two wires, right? I know the two sensors are near eachother right by the EGR; this one should have been the lower one.