WW Wiper dalay doesn't work

[P.E.Haiges]

After driving 2 days and over 1000 miles in constant rain the delay action does not work on my '80 300SD. If turned to position I, the delay position, the wipers run constantly like I had the control in position II which is regular low speed operation.

If I turn the wipers off and immediately turn to the delay position, there is about a 5 second delay until the wipers start, but they continue running with no delay between wipes afterward.

Anyone have any idea what the problem could be? Where is the device that controls the delay located?

P E H