Originally Posted by jwatson
Am I right in thinking the earth wire is the black one which I have removed the cap from? Attachment 97788
It is not easy to make out with that picture, and I am not too familiar with that engine, but if it is a black wire attached to the block then it is an earth.
If it were me I would be checking all earth wires that I could find, and any other connections just to be sure they are clean with no corrosion.
Sorry I can not be of more assistance.