Conversion question - single speed wiper motor to two speed wiper motor

[Blown66Mustang]

I am wanting to replace my single speed wiper switch and wiper motor to two speed speed switch and wiper motor so was just wondering if I need to alter the wiring harness for this to work? I have a 66 Mustang Hardtop, Thanks

[Bashfull]

hi,
unfortunately wehen i read the circuit diagram...
one extra wire to wiper motor.

why not consider intermtmewnt if going to do all that wiring...
dick smith use to sell a kit that would alow you to adjust the speed  form constient to intermtent and hide it just under the dash...