Earths and testing plug leads and extenders

[TV8]

Hi,

I have ordered a few bits and pieces and have some time booked-off to investigate my mis-fire (see other posts). I have read lots of posts about checking the earths and leads/extenders and wondered:
Where are the earthing points,
How do I test leads - the leads are stamped 5 ohms per metre and
How do I test the plug extenders.

Any advice or suggestions appreciated
Thanks in advance

Graham