Electric Fan Conversion Question

[RTLINGR2]

I’m in the process of electric fan conversion on my 03 Tahoe. I pulled the factory harness off my 05 Yukon. From what I can tell, I have thick blue/black and yellow/grey wires going to fans. Red for power. The 2 small wires blue and green go to PCM pins.

Question is, where is the black ground wire that bolts to frame? I never saw one as I was removing this.

Any thoughts would be appreciated!

The factory fan harness grounds the fans on the frame rail behind the driver side front bumper.