Like the engine wiring harness, the power wiring harness also degrades due to the age of the vehicles.  Although not subject to the high ambient heat of the turbo, this wiring harness, which runs alongside the driver's side of the engine bay, can be damaged by prolonged exposure to spilled motor oil.  Engine oil can be spilled inadvertantly by engine oil refilling or oil filter removal.  Failing o-rings on the oil filter pedestal can also leak oil onto the wiring harness.  Due to the close proximity of the spark plugs, the power wiring harness is easily jostled by routine removal and replacement of spark plugs or spark plug wires.  Bad spark plug wires can arc into the wiring harness, which could lead to major damage to insulation, wiring, or delicate electronic circuits and sensors!

Connections to all major power components are of high importance.  Check connections to the alternator (rear) and to the battery - if these are not secure, sporadic power connections can cause weird electrical problems.  Inspect the batter terminals very thoroughly, as battery acid can quickly eat through copper wiring!  Lots of nasty electrical problems can usually be traced to bad or loose battery terminals.  It wouldn't hurt to even change you battery terminals just as a maintenance issue.

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