My fans only turn on after I turn the car off. I think its the temp sensor. Is it the one on the waterneck or thermostat housing?

 

The thermostat housing in the back passenger side of the engine. It's normally called a "fan switch"

 

The thermo-switch A (aka fan switch A) is located on the thermostat housing (connected by the lower radiator hose). Normally, when the car is on even if the A/C is off, when the coolant temperature reaches ~ 194 degrees at thermo-switch A, both fans (A/C condenser fan and radiator fan) should turn on. If A/C is turned on, both fans should run regardless of the temp. at thermo-switch A.

After the car is shut off and if the coolant temperature at thermo-switch B (located at or near the upper coolant hose housing on the engine block) reaches ~ 223 degrees F, then the radiator fan come for a set amount of time.

 

...but not longer than 15 minutes due to fan timer.