I used one of the kits from Revolution Electronics: Intermittent Wiper Module | Revolution Electronics

It was inexpensive, easy to install. It works even with my hidden wipers, though its controls are somewhat limited; you have to cycle through the speeds. But no mods to your wiper motor or dash switch.

 

The Newport worked great on my 71, just added one to the 64 daily project.

https://newportwipers.com/product/1969-71-chevy-chevelle-non-concealed-park/#wiper-motor

 

Many years ago Radio Shack sold a delay/intermittent wiper module kit for I think $15.00. I built two of them and both worked well.

 

I had a JC Whitney one mounted in the overhead console in my 1981 Dodge Van. Only the actual knob was through the panel. (along with CB, Programmable Horn, Fog/Driving light switches, digital clock...)

 

You could keep your original motor and wire in this circuit. Been planning to do it on my car, but I've gotten to the point where I'm not driving it in the rain anymore. Hate seeing the rust spread.

http://www.techlib.com/files/wiperkik.pdf

 

That is the same basic astable multivibrator circuit for the Radio Shack unit.

 

I still have the guts of one in my tool box, I need to find it, maybe add it in. Would be nice to control it with a repurposed factory knob or something so it looks hidden/factory, not an add on knob under the dash. I never plan on driving in the rain, but it happens, and the 1967 wiper knob is almost easier to reach through the steering wheel to get to than around it. On, off, wait... On, off, wait, On DAMN TURN, Off, wait...

 

Here are some ideas as well.

https://store.qkits.com/automotive/wind-shield-wiper-timer-module-mxa041.html
[ame="https://www.amazon.com/Windshield-Wiper-Timer-seconds-MXA041/dp/B00W3IX5QS/"]Amazon.com : Windshield Wiper Timer Car Motor 3-30 seconds 12VDC [MXA041] : Everything Else[/ame]
https://store.qkits.com/automotive/screen-wiper-robot-kit-k2599-velleman.html