So I'm in the process of installing a 140 mph cluster in our T/A. Now I have a question, the pinouts for the 85 cluster have "BUFFER SIGNAL TO ECM" and "GROUND FOR BUFFER TO ECM." I will be installing the buffer box that came from an electronic speedo car. Obviously the brown wire that come from the buffer box provide the signal I need, but there's only 1 brown wire coming from the VSS Buffer box. What is this "GROUND FOR BUFFER" supposed to be hooked into?

 

Any connections that you know should be there such as power, & ground, and can't see are integral to the PC board traces and connectors, separate wires can be for short runs, or add-ons.
The ECM may not have existed when the buffer box was designed into the instrument panel printed circuit board.

The VSS signal is also shared with the cruise control module.