Can't believe you managed to read that drivel 
Odd tail lights problem!?
The stud isn't connected to the chassis (electrically), it's just a big terminal for bringing together loads of earth wires. I think the "bush" is actually a rivnut, though it could be a rawlnut - i.e. a threaded rivet that gets fixed into the ECM backplate. The ECM backplate is connected to the longeron (thing that supports the boot), which is connected to the subframe, which is connected to the chassis. So while the ECM backplate may be a source of a reasonable 0v reference, you wouldn't want to pass any significant current through it.
The chassis rail is earthed via the front earth strap.
The engine bay earth strap routes that to the gearbox for the engine earth (heavy duty starter and alternator currents).
The loom also has a couple of earth pickup wires in it that strap to the engine bay earthing point. These wires run backwards to the -ve binding post and provide the earth; all the other wires on the post are then picking up that earth again. The reason for using two wires from engine bay earth stud to -ve binding post is just to carry enough current.
Cheers,
Robin
The chassis rail is earthed via the front earth strap.
The engine bay earth strap routes that to the gearbox for the engine earth (heavy duty starter and alternator currents).
The loom also has a couple of earth pickup wires in it that strap to the engine bay earthing point. These wires run backwards to the -ve binding post and provide the earth; all the other wires on the post are then picking up that earth again. The reason for using two wires from engine bay earth stud to -ve binding post is just to carry enough current.
Cheers,
Robin
I is in your loomz nibblin ur wirez
#bemoretut
#bemoretut