This is an old subject for installing intermittent wipers. The old discussion involved using the factory switch and adding a delay box to retrofit. I didn't like the idea so I just settled for just doing without. I came upon this switch recently and was wondering if someone has or is willing to try it and report back. It's a plug and play solution using the same six wires to control low/hi speed wipes and press for spray plus two delay wipe speeds. It looks like it's been on the market for a while for other vehicles. There are applications that come with no or different connectors or buy the cheapest one and add the appropriate Feston 6-pin(?).
Here's an add I saw on eBay but the part is also available on line:
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