In the past I have thought this too, in fact I went as far as stripping back the wires to see how far the corrosion went..to help me in the future replacing the cables...I was staggered to see that it actually went as far as the bulkhead before pristine copper could be found. This may have been a one off, but this must have travelled all the way from the sensor end of the cable. I now suggest replacing well into the engine bay for longevity of the task in hand.