google me this: Potentiometer

If you need a pot, or just about any other electronic device, glance at digikey.com They've got EVERYTHING.

If you feel like fabricating, you may be able to adapt the intermittent wiper setup from an early 90s Buick, Pontiac, Olds.

A quick google search makes it appear the delay is part of the wiper motor assembly and the switch was a dash mounted set up with a slider for the delay, high, and low settings.

Maybe check the local pick & pull to see how far off it is from what you already have. I'd also bring a continuity tester to see where the wires need to go before cutting anything.

You may also find some useful info here: delay wiper primer

I have stacks of brand new old vintage tube radio potentiometers. I'm not sure of the values, but if you're looking for one I can see what I have.

Most cars now have self parking wipers. The self park works by having a constant power supply go through a brush, to a partial slip ring on the bull gear in the wiper motor gear box, through another brush, to the pos side of one speed of the motor. This circuit is independent of the switch, and you can test it yourself by pulling your wiper arm out of park; at some point it will sweep on its own.

If this circuit is functional, the speed of the actual wipe will be constant no matter what the switch rheostat is doing. The power from the switch only supplies power to the motor for a tiny fraction of the wiper sweep while the parking contact isn't working (at or very near parked.) That means the rheostat doesn't need to really be as big as you might think.

Does anyone know the difference between a potentiometer and a rheostat? I cant seem to figure it out.. read this article Rheostat Explanation
but it only explains briefly.

Noticed people were talking about potentiometers in this thread so thought I might have some luck... Ive been confused about this for years, I don't really see the difference between the two. 

Any and all help would be great !

Both are three terminal variable resistors with a fixed resistance between two terminals and a tap whose resistance varies with respect to the fixed terminals depending on the position of a mechanical device such as a knob or slider.  In general, the difference between a potentiometer and a rheostat is in the manner of construction.  A pot is generally a low power variable resistor that is constructed with a conductive film, usually some carbon based material.  A rheostat is a high power device that is constructed (as are high power resistors) in a wire-wound manner where actual wire of known resistivity is wound around a core in a single layer.  The movable tap actually touches the wire as it physically moves along its path.  A wire-wound resistor can handle a lot more current, and dissipate a lot more heat (power) than a thin carbon film.

I'm an EE, and can vouch for Stukndapast's post above.

For what the OP wanted to do, a PWM output is the right solution, not a pot. PWM means Pulse Width Modulation, and it works by duty cycle. If you want the wipers to go half speed, you feed it an on/off voltage with a 50% duty cycle, and so on.

You guys realize that this is now an 8-yr old thread...

Learning! Woo!