78 Chev Windshield Wiper Switch

My son has a 78 Chev 4X4 Pickup that does not have "Pulse" or delay windshield wipers. Does anyone know if you can convert over to a delay
one by just changing the switch? I believe that delay wipers were available as an option in 78. I've looked in several catalogs and they show just one part number for the wiper motor, which leads me to believe that it all might be in the switch module.
Any help is appreciated!
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