On Wed, 20 Jul 2011 14:09:41 GMT, (Doug
Miller) wrote:

In article , "m II" wrote:
WD-40 my be OK for a manually operate contact but not for an electrically
operated contact. We had a guy try it on a bank of relays and the whole
thing seized to halt!

Sure you did. Urban legend. Something you heard from a friend of a friend.

The stuff evaporates and leaves a sticky mess,

Garbage. It does nothing of the kind.

not to
mention where any arcing has occurred the result is pile of sticky carbon
and a flash that burns the contacts beyond usable.

That, of course, is the entirely *normal* result of an electrical arc
*without* WD-40.

A few mechanics have witnessed signs inside the hoods of`vehicles ``USE OF
WD-40 ON THIS ENGINE WILL RESULT AND NOT PAYING THE BILL OR LITIGATION FOR
DAMAGES``

If by "a few" you mean "zero" then this is probably true.
WD 40, when used as a lubricant on something originally lubricated
with grease, CAN remove the oil from the grease, leaving behind the
"soap" (sodium stearate in some cases, lithium in others, plus a host
of others)- which will cause mechanisms to stick.

As for electrical contacts - on sliding contacts like many automotive
switches, and at low voltage and current, not likely to cause much
problem - but any arcing in a switch with "oily" contacts WILL cause
carbon build-up - which CAN cause high resistance, heating, and
burning of contacts. High voltage and high current contacts must be
CLEAN or lubricated/protected by an inert grease (dialectric grease)
that will not burn and protects against corrosion.

Spray WD-40 (aerosol) has (or at least had) a flammable propellant,
which, if used on an arcing contact - or in proximity to an arcing
contact, CAN ignite - with rather spectacular result if, say, inside a
distributor cap.

There are NO manufacturers that plackard their under-hood areas with
prohibition against using WD40 under the hood.
It is EXCELLENT for drying out damp ignition wires - even though there
are better products, which help seal the wires against moisture for a
longer time - but NEVER use "ignition sealer" - the plasticy coating
if compromised at all, just traps moisture in the wire, making it
worse - and impossible to dry out with WD-40 or anything else.