Burnt out gearbox earth - cause or symptom?

[NeilinBrussels]

I have a 2010 Focus Diesel which will not start (Engine Malfunction shows on the LCD screen). On taking off the filter housing to look at the ground wires (seen in other posts as an issue) I found the wire from the top of the gearbox to the body has burnt through. Although this may be part of the cause of the problem, I would think that the burning of this wire (almost all the plastic around the wire is gone and the rest is crispy!) is not normal? Before I replace the wire and see what happens I would appreciate anything else to look at. Is there for example another earth wire elsewhere to look out for? 

Thanks. Neil

[Hearsepilot]

The connection will get hot if there's any resistance, it would be progressive. Just replace it all will be well.