Where is the fan relay switch located on a 1989 Cadillac Sedan DeVille?

I would check under the hood if I were you. Just a suggestion.

a location I experienced (second author on a 1989 coupe de ville here) is one or some of the three relays a few inches from the battery connections and I heard there may be one near the glove box or fuses inside the car (I tapped on a stuck one of the three to get the cooling fan to go off)