That's the overtemp sensor that turns the high fan on at 220. Will also run with the car off if 220 up temp is present. It's left many people with a dead battery in the morning when it craps out .You might need this switch. It is in the front of the intake on the driver side. It has one wire going to it (green I think).
http://www.oreillyauto.com/site/c/detail/MPI0/28386/01963.oap?year=1987&make=Buick&model=Regal&vi=5000098&ck=Search_cooling fan switch_5000098_1596&keyword=cooling fan switch
When my switch failed, fans came on around 220 and then shut off around 200. Was very frustrating until I figured it out.I bet that's not what it is though. It's rarely ever that switch.