Windowscreen wiper mod, help needed please.

[potato head]

Hi,

I'm looking to make a mod to my wipers on my car. At the moment my wiper switch has 3 positions, on normal, on fast and just a mom on for a single wipe.

What I would like to do is have a new switch in addition to the wiper stalk on the steering wheel column that would let me run the wiper through a variable timer / capacitor so I could flick the switch on then control the wipe delay speed to suit the conditions.

I have however, no idea how to do this or what parts I need.

Is there anyone that can help me out?

Thanks.