Kickdown Harness $32 mail order (appx.) various vendors.
Kickdown bracket & throttle lever (paddle) $39 (appx.) Ebay The Parts place.
Kickdown Switch (Used or NOS) $ (??) swap meets-epay-ads.
The nice thing about the switch which is NOT reproduced is they applied this switch & similar versions on TONS of body styles, across the GM lines Trucks also, so your search will not be that difficult.
Couple notes:
I think the Yellow HOT (+12V) feed is from the Wiper motor. to accomplish properly you need to extract the female spade connector and replace the terminal with a double wire version and re-insert to the plastic molded connector. (Disclaimer this is how LOS wired my orig 68 L35/TH400).
This is where I purchase my terminals & use a special crimper.
http://www.texasindustrialelectric.com/_packard_terminals.aspThere is also a steel wire harness clip that retains the harness using one of the transmissions housing bolts to route harness down the back towards the kickdown solenoid. & clip on side of TH400 trans.
Consult your assy manual for lots of installation details.
JIM