Yes cool harness works but its just a sresistor. But it does just mask issues. After thermostat there will be air in the system make sure you get out all you can. There is a resistor block under the ABS area that can become corroded and make the fans stop working. Also you can jumper the leads on the A/C dryer (with a/c on of course lowest cold setting) and the 2 wire temp sensor on the intake to test for fan operation to force them on. I found when I had to put in my new radiator the fans came on less because it was so efficent compare to the 17 year old one that crack finally and that proper pressure cap kept system cooler and fans almost never come on except at idle stopped at a light with the A/C on as that is what they are supposed to do. The motor temp for them to come on is 105 degrees so unless it gets way up there you shouldnt see them come on at idle (unless you jumper the sensor for proper operation or use cool harness).