Primary Ground for Dash Harness?

Do our cars have a primary ground lug for the harness under the dash? I can see a pair of heavy gauge wires near the fuse box, but can't see where the one, presumed to be ground, goes.

Recently, I noticed the tach needle moving when I press the brake pedal and want to confirm all grounds are making good contact. I also observe the tach signal on DAQ data that only shows up when on the freeway.

If any of you knows if/where the under-dash harness grounds and where that's located, I'd appreciate it. Pics are a bonus.

There are 2 main ground points: one on the far passenger side (single wire ring connector) and another above the glove box with 2 wires. Ground to dash is supplied by one of the dash connector pins.

Here’s pictures of what Midlife describes. If you’d like more pics let me know because my dash is out and I’m refurbishing it. I can easily snap more of what you might want.
Bob

Thanks guys, much appreciated.