Coolant Temp Sensor Connector


May 22, 2013
Today I moved on to the next issue with my car. The gauge for the temperature shows above 270 all the time. I noticed that the sensor on the black line coming from the water pump was broken in half. I bought a coolant temperature sensor and when I went to remove the old one, I noticed that there were two almost identical plugs, the only difference was the squared off portion for the sensor. So I replaced the coolant temp sensor, but wondered what goes into the other plug. I read some posts and it says the ACT goes there, but then another talks about the ACT is in the Mass Air Flow, which I have on my car. So my two questions are, do I need to hook the ACT sensor up to the connector, and if so, where does it go, as I do not see a spot near where this connector can reach. Second, I learned that the gauge inside is controlled by the temp sending unit, which I found behind the distributor area. Is there a way to test this to determine if its bad, like the resistor test for the fuel sending unit? Thanks in advance for any help, you guys have already helped me solve so many issues with this car.
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This is the temperature sending unit, mounted in the lower intake right behind the distributor



Here is the coolant sensor unit (ECT) that normally screws into the steel pipe for the EGR coolant line or directly into the boss in the lower intake on the passenger side


Here is how they are normally connected



The ACT/ IAT measures air flow and the stock location is in the#5 runner of the lower intake> Yes it needs to be hooked up.


Now that is all cleared up, the temp gauge works off the sending unit- the one screwed in behind the distributor. To see if the one installed is bad, with the key on but the engine OFF disconnect off the sending unit connector, and ground it to a bolt on the engine or chassis. Go look at the gauge. It should go to all the way up to HOT. If it does, 99.99% the sending unit is bad, not the gauge. They are like $5 so it's a cheap fix. Wrap some teflon tape or paste on the new one to avoid leaks.
Thanks for the detailed information! I was able to locate the ACT, I was looking in the wrong spot. So I have all 3 connected (ECT, ACT and Sending Unit). But now my question is the connector seen in this pic I took:


The connector is connected to the ECT (coolant temperature sensor), the other connector, just to the right of the connected one, looks almost identical, except the part that is squared off is on the opposite side of the connector (left/right). I thought this was the connector for the ACT, but I found that connector on the other side of the engine (see pic below)


So, is that loose connector supposed to be connected to something? I know the car has had addons done to it, so I am not sure if anything was removed. As always, thanks for your help, your above post let me find the ACT and is putting me on the right track.
Here you go...


It is probably the connector for your canister solenoid mounted on the passenger side framerail. The connector is attached to a long wire with a connector on each end. One side goes into the connector by the ECT, and the other plugs into the purge solenoid.

Wire with plug


Purge solenoid (disregard the cut wires as that was for a fan install)