th400 downshift switch wiring? - The BangShift Forums Re: th400 downshift switch wiring? It started earlier in Buick's I think but I'm familiar with that set up since it's on my '64 Nailhead. 2 wires, hot to the switch and then out down to a single blade terminal on the side of the transmission. Transmission grounds internally to fire the solenoid when you give it +12V.
Related with turbo 400 transmission wiring diagram