Eric,
  I don't know if you have any way of studying the diagrams in the Bentley,
but what Neil said is correct.  The smaller of the two wires at the
positive battery post leads to the fuse/relay panel in front.  It is
unfused to that point.  If it is disconnected there will be no life in any
of the accesories, or the ignition and ECU for that matter.

Larry A.

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