Some help please, GT's dead.

[jooshy63]

Need some help please, I'm losing my marbles trying to figure out why the GT isn't starting.
I'm assuming it's something to do with electrical wise as when trying to tick over, I get nothing.
At first I thought it was the starter motor gone so I replaced that only to have the same problem, nothing, not even a tick bar the fuel pump working.
 The only way I can get it started is by bumpstarting or strapping an earth lead from the battery to the engine block. The only thing I can seem to narrow it down to is a dodgy earthing point somewhere, I've replaced the earthing cable from the battery to the inner wing in the hope this would solve things but still, I have the same problem.
 I've looked at the wiring diargram for the starting and charging system and found three earthing points, one going to the body (which I've replaced) One in the headlight wiring loom (Which I can't seem to find) and the last one on the inlet manifold, (again which I can't seem to find).
 I replaced the standard headlights with HID's last week and wondered whether this could be anything to do with it, even though the car was fine up until yesterday.
 I'm baffled as to what it could be, could one of the mentioned earthing points affect the engine starting if it's loose, corroded etc?

 Help Please!

[hayesey]

yes if the engine doesn't have a good earth then it wont work at all. 

How about the earth strap from the top gearbox mount to next to the ignition coil?  Or the one on the cambelt end engine mount to the chassis rail?  Or the starter itself has a large earth going directly to the battery

[Puncharado]

Yes, rusty and corroded connections on the alternator/starter/battery loom can cause this, I had the same thing with a mk2 Golf. Got the sandpaper out and cleaned up the lot, and the earth to the engine, covered them in grease to stop further corrosion and never had another problem.

[jooshy63]

Thanks people, was a bad earth, thanks for the help.