There's one under the bonnet fixed to the clutch or brake master cylinder cover plate.i forget which.
When I had gauge and iirc indicator problems years ago it was the earth wire there that I had forgot to reconnect after doing a job.
It's a herf and can go to henni huvver herf, even te twon nexter it.
Frum tlucks uvvit it cud go ontert reetand gage herf clamp, coz it lucks baht wun ... an it Sundi
Crimp another ring terminal on it and pop it on the one next to it and then run a fesh earth wire down to a known good earth to ensure you're getting max earthing
