[hatzie]

At least one wire from Splice 150 should go to the Ground buss bar above the E-Brake Pedal. If you don't have one then it's probably what got cut off.

GM used a ring terminal on the bolt connecting the buss bar to the kick panel sheet metal according to the diagrams.

Some possibly helpful trivia on the diagrams...

Notice the Delphi connector shell part numbers for each and every electrical connector are right next to the terminal in the drawings?

This is how you can tell from the above section that the Tach and Clock used Delphi 12004267 Packard 56 connector shells to connect to the ground buss bar. Looking up the connector shell online will tell you what family they belong to and from there you can find the terminals to crimp onto the wire. Mouser Electronics has a lot of Delphi connectors listed even if they don't stock them. They also usually have links to available data-sheets.
GM bought into the whole "were going Metric thing" so the conductor diameter isn't listed in AWG on the GM wiring diagrams after 1978 or 1979.
Just before the wire color circuit number tables you'll find a mm² to AWG table.
The conductor diameter is called out in mm² immediately preceding the wire color which is followed by a dash and then the circuit number. The ground circuit you're chasing says .8 BLK-150 Translated---> .8mm² (18AWG) BLK (BLACK) - Circuit 150 (Ground).