Trev,
I suggest then having solved that that you look at all the other earths. You really need to take them apart as the corrosion is not always visible.
Here is the Roadster set up.
https://www.gomog.com/allmorgan/Roadster_earth_grounds.html
John


JohnV6
2022 CX Plus Four
2025 Renault Scenic Alpine etech "Yvette"