New here to the forum and new / old deville owner. Just picked a very nice 1970 coup deville convertible. Engine and nearly all systems rebuilt and working fine. My issue revolves around the wiper system and I think specifically to the switch. I have done a search but did not see this particular issue discussed

symptom - slide the wiper control to any of the three speed settings and nothing happens. Press and hold the "wash" button and the wipers work at all three speeds. Release the wash button and the wipers retreat to their parked position.

I ordered an "untested " switch from eBay and it didn't work so no definitive answer bit it seems it must be the switch or maybe a frayed wire along the path. I haven't found a wiring diagram yet but thought I'd check to see if anyone has experienced this issue. Thanks