A few months ago I asked for help on this list with a sporadic starting
problem.  The problem only occurred every several days, or even weeks.  The
symptoms were no turnover, no click, nothing but the fuel pump running when
the key was turned to start.

Several helpful suggestions were made from this list, including cleaning the
battery posts, but none worked.  It might be interesting to someone to know
what the problem was and how I diagnosed it.

The starter motor had been replaced in less than a year before, so it should
have been fine, but my mechanic suggested I do this, in order to diagnose
the problem.

I temporarily ran a wire from the hot lead of the starter motor.  This led
up beside the driver's seat to an indicator light....the kind you can get an
any auto parts store to find live wires or shorts.  I grounded the other
conductor from the light on the seatbelt anchor.

When the key was turned, the indicator light should come on, and did, as
expected.  But when the no-start problem occurred, by looking at the light,
I could see what was going on.  If the light was NOT on, as usual, that
would mean no current getting to the starter and the problem was most likely
in the ignition switch.  If the light WAS on, then current was getting to
the starter, but it wasn't responding, so the starter was bad.

Result: The light was on and the mechanic replaced my starter on warranty
without an argument.