Repeated from Ford Focus forum.

Can anyone please identify which cable goes to the bolting point in the rear, right, lower corner of the cylinder head. 

I may be going senile. I'm refitting the engine in my daughter's car and can't find the connector!

This position is very difficult to see with an engine installed but hoping someone here remembers it or has it visible.

I think you should find the other end of that connected to the chassis earth point underneath the battery tray.

Thanks Unofix. Will remove the battery tray and take a look. Can't understand why I can't just see it. Maybe I pushed it back too far when I disconnected it from the head. 

Have already connected the main earth cable to the front of the bell housing and a smaller earth cable to the front corner of the cylinder head (underneath the vacuum pump).

Why there would need to be another cable from the chassis to the head evades me. I assumed from the size of the chopped off cable in the screenshot that it was part of a loom.

In actual fact it's not needed so long as the main engine bell housing cable is connected. These extra cables are quite often fitted to help meet the EMC regulations on electrical noise interference.

Earth ring terminal and associated wire found. Situated at the position on the loom where the two exhaust sensors plug in.

Had trapped it behind the starter cable bracket that piggybacks to the top of the starter motor.

Unable to see where it comes from as wrapped with other cables.