For example, we sell a that has 185/170 temperature sensor (illustrated below). This item will activate fans @ 185 degrees.
Issue: Many vehicles come with a 195 degree stock thermostat.
Running this item with a 195 thermostat would result in the fans being on at all times. Why? The vehicle will be maintaining a 195 degree temperature and the sensor will then think the vehicle is hot at all times and keep the fans kicked on.
This presents an issue. Why would you need a sensor wiring when the fans would be on all the time? Answer: you would not! If you will stick with a stock 195 degree thermostat, then you will not need this type of wiring. You can then just use straight single or as pictured below.
If one wanted to stay with a 195 degree thermostat, they can swap the sensor in their wiring to a high activate temperature. below is a picture of a that is set for 195 degree activation.