Coolant temp sensor

You only have one. It should have two wires; a black / light blue and a tan / black. That's the sensor for the Engine Computer. Instead of using a second single-wire sensor like they did previously, the information is transmitted to other computers over the two-wire data buss. The instrument cluster is a computer module that reads that information and gets it that way instead of using its own coolant temperature sensor.

Is that relay you changed a four-wire electronic unit halfway down the left side of the radiator? Use an ohm meter at the connector to measure the resistance of the black wire to ground. It should be real low. That is the relay's ground wire. Next, check for 12 volts on the gray wire. If it's missing, check fuse 106, a large 40 amp.

If both of those circuits are good, measure the resistance of the 12 gauge dark green wire to ground. There will be some resistance because you'll be reading through the two fan motors, but the resistance will be pretty low, in the neighborhood of an ohm or less. You can also apply 12 volts directly to that wire from the battery positive post. If the fans run from there, you know that wire and the motors are okay. That just leaves the circuit coming from connector 2, pin 73 of the Engine Computer. The Chrysler DRB3 scanner would be very useful to command the computer to turn on the fan relay. If the fan doesn't turn on that way, suspect a computer problem. If it does turn on, use the live data screen to view what the computer is seeing for coolant temperature. The fan should turn on at 210 or 212 degrees.

On older models, the fan would turn on if you unplugged the coolant temperature sensor while the engine was running. That was in case the engine was overheating and the computer couldn't tell. The Check Engine light will turn on and a diagnostic fault code will be set in the computer, but the light will go off when you plug the sensor back in, and you may have to restart the engine. The fault code will erase after a while on its own.