On Sun, 2 Jan 2011 14:40:01 -0800 (PST), Andy Dingley
wrote:

On Jan 2, 9:02*pm, Roger Mills wrote:

As others have said, it's pretty certainly an earthing fault.

You can diagnose rear light cluster earthing faults quite easily -
look for a Ford or Renault badge. However they make them, they haven't
got reliable earths to the rear clusters.

It would probably be much better to use a wire "earth" return, rather
than rely on the chassis.

--
Frank Erskine