Again not knowing your vehicles specific setup and layout I’m just taking shots in the dark.
When you say:
” We checked the relay connection in the fuse box with a circuit tester, 2 of the power pins & 1 ground pin sends steady connection, but when testing 1 ground pin, the tester flickers on and of as if there wasn’t a steady circuit/signal.”
Is this happening when just the know good headlight is plugged in?
Or does it flicker only when you plug in the affect light?
My guess is if you have a steady ground when the good light is plugged in and a flickering ground when you have the faulty light.
That would narrow it down to the electronics on the faulty light causing the issue.