GoMog as a website has a lot of useful info. This is where the earths are on a later Roadster but I expect your car to be similar.
Some fuel pumps have separate earths.
"Here are the major grounding points on the Morgan Roadster (USA). These may be identical, similar or not at all like the ground on the late model +8s of the same vintage or the other world versions.
1. Behind the Fascia there is a ground terminal on the heater box. Suggest moving this to the scuttle bar.
2. Engine had a ground strap to the scuttle (firewall).
3. Engine computer, inside the fuse box, a wire runs to a bolt on the bottom of the fuse box.
4. Outside of right hand valence (remove the right front wheel) near the air intake tube.
5. On the rear chassis member near the right rear wheel.
6. And of course, the chassis to battery ground. "
