The best place to get the missing heat sensor -- actually more like a thermo-switch -- is at a salvage yard. If you have the aux. fan, and you probably do, you need the switch to activate it. Pick one up at a salvage yard for a couple bucks and just cram it in the hole. A rubber grommet hopefully already in your radiator holds it. Then connect the two wires with the female connectors that you found near your battery. You can test to see if your fan works by running a jumper across the two wires before you connect them to the switch (ignition switch has to be in "on" position). Also, don't be surprised if the fan never comes on under normal driving conditions. The cooling on the 740's is very good, so unless you are towing, the coolant may never get hot enough to cause the aux. fan to came on anyway.