HELP--Coolant sensor in coolant bypass block
 

Hello all,

I bought a 93 4Runner with a blown head gasket, a 3.0. I replaced the gaskets and now cannot find a specific sensor wire--I know it sounds ridiculous. Anyway, the sensor is on the coolant bypass block and is round and a blueish color. Does anyone know what this sensor is for? I believe the wire should come out of the wire harness running down the driver side of the engine--with the injector wires and other coolant sensor wires. The problem is the wire is not there. I'm pretty sure I took it off--been a few weeks since I disassembled it--and the sensor looked clean like it had been covered so I'm assuming there was a connector on it. I have stripped the coating off the wire harness back to the front of the engine and cannot even find a broken wire. So my questions are, what is this sensor for, will it run without it being hooked up, and anyone know what color the missing wire is? Pic below of the sensor in question. Any suggestions would be greatly appreciated. Thanks