Mine is a 76, but...
The earth lead from the battery and an earth lead from the manifold bolt closest to the firewall are BOTH connected to the chassis at the firewall, about 2 inches (5 cm) to the left of the battery. They share a bolt on the firewall just above and to the left of where the temperature sender and choke cable come through.
I hope this helps!
On their death bed, nobody ever said, "Gee I wish I'd spent more time at work!"
'68 Sprite 1275
'76 Midget 1500