Blower motor black wire is the ground.
Goes through splice S806 to Ground G130.
S806 is in the A/C harness behind the blower motor manual picture 201-19B, which appears to be a couple of inches inside the harness to the right of the blower motor.
G130 is behind the R/H side of the Instrument Panel figure 201-20-A, which isn't really shown for the turbo motors but it appears to be back inside the car and should have a self tapping screw through an eye a 12 gauge all black ground wire.