Re: More Ignition Switch Woes

[jlandry@domain.elided (John A. Landry)]

In a brilliant stroke of genius, "Joseph M. Shaw, II"
<MikeIIDC@domain.elided> blurted out:

>I am the one that had an ignition switch problem.  Would work fine for
>about ten starts (while diagnosing a fuel problem; I wasn't just sitting
>there seeing how many times it would work!), then would completely stop
>triggering the starter.  Lights would still click on, but no start. 
>Then it even started continuing to turn the starter after I turned it
>off.  I took the switch off and went to Pep Boys.  The truck is a '74
[snip]

Mike,

This sounds like a classic starter solenoid failure.  The starter solenoid
is mounted right on the starter.

When you turn the key, an electromagnet is energized in the starter
solenoid which pulls a large copper disk into contact with two large high
amp electrical terminals.  When these terminals are bridged, electricity
flows to the starter motor directly from the battery.  So the ignition
switch in (or under) your dash only supplies current to the
electromagnet... obviously not the starter motor itself. 

In time, the large copper disk inside the starter solenoid gets burned,
pitted and gets a buildup of carbon from all the arcing of high amperage
electricity.  It's pretty normal for an older solenoid to start having
problems when the starter is used repeatedly, even more so when the starter
gets hot.  The copper disk is designed to rotate slightly each time it
makes and breaks electrical contact.  This gives the solenoid longer life
and keeps the disk from rapidly getting burned in one spot.

If a particularly badly burned or pitted area on the disk is lined up with
the terminals inside the solenoid at the time you turn the ignition key,
the result is that electricity isn't passed to the starter motor and
nothing happens.  In some circumstances when the starter is operated for a
long period of time and the solenoid gets really hot (and possibly the
copper disk inside the solenoid is particularly nasty and pitted), the disk
can actually become welded to the terminals inside the solenoid.  There's a
spring inside the solenoid that is supposed to push the copper disk away
from the terminals once the electromagnet is no longer energized by the
ignition key.  If the terminals get welded to the disk just a little bit,
the spring may not be able to separate the two.  The result is the starter
motor staying energized even though the ignition key is released.

You can replace just the solenoid on the starter for maybe $15.00 or less,
or you can go ahead and swap in a complete starter / solenoid assembly.

Happy New Year,

John L.
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