Changed the thermostat housing on my 02 4.0l ford ranger because it was leaking. One of my sensor wire plugs had to be replaced but I was unsure how to wire it because both wires were black. Now my truck doesn’t leak but will not cooldown at all unless I turn off my truck. Is this because of the sensors wiring? Thanks

 

The ThermoStatHousing on your 2002 V6~4.0L~SOHC should have 2 TemperatureSensors:
one with the 2pinOrange harness connector goes to the InstrumentCluster\TempGage,
the other with 2pinGray harness connector goes to the PCM\Computer.
These 2 ThermoCouple Sensors are electrically different, NOT interchangable, & the connectors should be keyed differently.
If the wrong sensors have been installed\used &\or the connectors have been erroneously modified, that may be your problem.
Considering you just replaced your ThermoStatHousing & ThermoStat?,
you could have installed the wrong ThermoStat or it could be stuck closed, causing the overheating.
Are you monitoring the Coolant Temp with just the InstrumentCluster\TempGage?
Recommend also using an OBD2 Scanner to look at Coolant Temp via the PCM\Computer.
Is the upper Radiator hose coming up to operating temp ~5min after starting?
Hope you installed a new ALuminum TStatHousing & not a JunkPlastic version?
Click here for more info on the TStat+Housing+Sensors for the V6~4.0L~SOHC.

 

The two "sensors" on the thermostat housing are not the same

One is an ECT sensor, 5volt, and only used by the computer, will have a green and grey wire
Other is Temp Sender, 12volt, and only used by dash board temp gauge, has red and black wire

From your description you either got the wrong temp unit or connected it wrong, my bet is wrong temp unit
Parts stores will ALWAYS sell you an ECT sensor, not sure why but they do
You need a temp S E N D E R, sometimes spelling it will help, lol

If you are not sure of the wiring or if the connector has been replaced, i.e. 2 black wires, then you will need to test the wires and the sender

Simplest thing to do is make sure you got a SENDER, look at the part number and then look it up, it will say sender not sensor
Senders usually have a cylinder shape tip that goes in the coolant, sensors a cone shaped tip, but not always

If you have a sender then plug in the connector and turn on the key, engine off
If temp gauge goes to HOT turn off the key and REVERSE the wires on the connector
Turn on the key again and it should stay at COLD
Start engine and it should should it warm up normally after 5-8min and stay just under 1/2 way point, 190degF, 1/2 way is 205degF