"DoN. Nichols" wrote in message
...
On 2014-08-04, Jim Wilkins wrote:
"PrecisionmachinisT" wrote in
message news:IZGdnULFVopIgULOnZ2dnUVZ_uidnZ2d@scnresearch. com...

"Jim Wilkins" wrote in message
...

The other day my truck had a no-start problem that turned out to
be
a poor cable connection at the battery clamp that I'd missed
during
an otherwise thorough spring electrical cleanup. I found
it -after-
I had removed, disassembled and thoroughly checked the starter.

The corrosion hidden inside the cable clamp still allowed about
30 - 40 Amps, not enough to spin the starter motor with the
Bendix
engaged but the voltages were correct everywhere that was easily
accessible, the solenoid clicked and the battery dropped to
11.5V.



Suggest next time feel the cables and connectors first, when this
happens usually something gets hot.

When something electrical malfunctions my experience-conditioned
reflex is to mentally photograph the symptoms and then quickly shut
off before something gets hot enough that the expensive magic smoke
billows out. I use the IR thermometer or as a last resort my hand
to
chase less dire emergencies.

Without the high current, get a voltmeter and stab one probe
into the battery terminal and the other into the terminal clamp. If
you
get *any* deflection of the needle (or reading on the LCD display)
that
means a poor connection through the terminal/clamp interface.

I've been known to get people home by putting a large wood screw
between the terminal and the clamp at the split. That bites well
enough
to get them home (or to a place which will clean/fix it) without
needing
to call a tow truck.

The stainless steel pocket knife I carry isn't harmed by scraping the
terminals clean or prying open the vent caps. It doesn't hold much of
an edge, but the triangular needle file in the tool kit will
temporarily let it saw through thick nylon rope.


I did jump the relay with a screwdriver and heard the starter click
but not chatter, the usual indication of insufficient current from
the
(12 year old) battery. Mostly I checked meters set up on the cowl
to
show voltages and current while I turned the key. Seeing up to 40A
in
the cable to the starter and still 11.5V at the clamps mislead me.
In
the spring I had thoroughly cleaned, labelled and Ox-Garded all
engine
compartment electrical connections (except this one).

:-)

Enjoy,
DoN.

11.5V from the (+) terminal clamp to a ground screw on the inner
fender was misleading. It showed the battery was capable of supplying
current and the (rebuilt by me) starter was drawing some but not
enough. The dash lights dimmed only a little. The first thing I did
was recharge the battery. The automatic charger shut off within a few
minutes, ruling out an alternator (also rebuilt) problem.

I've described only the symptoms visible from the engine compartment
and cab, mostly as voltage, to add to the list of things to check
beside the road. I don't expect most people to have a DC clamp-on
ammeter probe for their DVMs.

The problem was obvious when I crawled underneath and clipped a longer
meter lead to the starter solenoid terminal. The voltage on the heavy
cable from the battery dropped from 12.5V to 0.2V when I turned the
key. Hmmm!

-jsw