Ignition wires age and fail. Some are defective even when new. It only takes
a pinpoint failure of the insulation to cause a miss when carrying 25,000
Volts. And there is no simple way to inspect for that -- the common
resistance test tells nothing about the quality of the insulation. Those
things just present themselves one day. Sometimes simply manipulating the
wire when replacing a plug will make the problem appear. It happened to me,
except that I had no dealer to blame - it was me doing the work. Many will
recommend replacing plug wires as routine maintenance, similar to changing
For all those reasons, newer cars use COP - a coil per plug arrangement,
with no high voltage wires (though they seem to have problems of their own).
That much said, $270 for just replacing a set of plug wires is unreasonable.
Even at the dealer's price, a set for my V8 Explorer was less than $100. And
it should not take a skilled mechanic more than 1/2 hour to do the job. If,
however, it required some diagnostic work, scoping the ignition, etc, it's
probably not that out of line.
As consumers we have a choice: I have the tools and manuals and troubleshoot
my own cars. You may do the same. Or you can shop around. The independent
mechanic down the street may not have all the fancy equipment, the courtesy
van to take you back to work, or the slick service writer in suit and tie,
but he is probaby still well qualified to change oil and replace plugs. And
he will be happy to install aftermarket wires which cost half the dealer's