I worked as a Ford partsman from 1978 to 1992, and agree with what cucumber has told you ... "17C476" was the ford basic number for a wiper delay module. (NAPA and Blue Streak DO call them a "relay" though)
If you go to Bluestreak's Online Catalog
and then click on the cross-reference tab. Enter "17C476" into the text-box, and then click on the "contains" selection and press [Search]
The way to tell for sure is by the look of the switch. The "interval wiper" switch had an addition external wire lead on it.