ECU box ground.

IMO; a grounding wire is a waste of time.
But I did BOLT my box to the apron when I was using those.
If you run a separate wire, you still have the exact same problem area; before you installed the wire, it was box to apron/firewall; after the wire, it is box to wire; no difference unless you weld the wire to the box. Just make sure your passenger head is grounded to the firewall and you will be fine.

For a long time, I had two of them bolted to the apron, so I could just swap boxes in a few seconds; then replace the faulty one after I got home.