Make sure is really a Fan Switch...
Many confuse w/ other senders/sensors especially old type ECT for ECM that Doesn't Ground to case and read "Open" tested for that. But Will get ohms between "pins." see cave ECM section.
New style ECT use newer Metripack connector and plug looks way different but only 87-88 duke and maybe 88 V6 came w/ it as factory install. Others have them because can't get old type to replace "dead" units.
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Dr. Ian Malcolm: Yeah, but your scientists were so preoccupied with whether or not they could, they didn't stop to think if they should.
(Jurassic Park)
The Ogre's Fiero Cave