I have replaced the original switch with a on off on toggle switch. I can have earth from wiper to off position and one speed to one on and the park wiper to the other on and I have one speed only and flick to park,
or
I can have off to earth, low speed to one on and high speed to the other on and that works but then I have to manual park by flicking toggle.
and
I have tried to put the park wire on all 3 positions and I blow fuses.
I don't quite understand as when you look at the original set up it seems simple,
or
what will I do?
thanks Jim

Why replace the original switch?
 

The park fuction is a fuction of the wiper motor, try a different wiper motor, the funtion is it keeps power to motor until the gear section breaks electrical contact.

Hi Jim.
 
What you need is a double pole on-off-on switch (DPDT).  You connect off to earth, low to one of the on's and hi to the other on.  All this is on one pole.  You then connect the park earth using the second pole so that when the switch is in the off position it is connected to earth.  As below:
 
 

 
Hope this helps.

Thanks Mk1_oz

Just on this (I'm looking at upgrading the switches in my van too) - do all Mk1 wiper motors have a self park function?  At the moment I have to flick the switch off when the wipers get to the right position! 

Pretty sure even the single speed units had self park

Cheers for that - at least I know that I'm chasing a fault rather than just a missing 'option'!

The fault is in the wiper motor

IF you carefully take apart the wiper/motor assembly you can clean up the three (?) contacts and the rotating plate.  This isnt a picture of an escort unit but it might give you an idea (I borrowed this from a random website but appears to be from this forum!!);