On Tue, 06 Apr 2010 23:49:41 +0100, goofball_star_dot_etal
wrote:

On 06/04/2010 21:33, goofball_star_dot_etal wrote:
On 06/04/2010 21:04, Armond Perretta wrote:
My 2002 (1993) has 3700 hours and runs well. The deluxe panel also was
fine
with all gauges except the tach performing properly. I have replaced the
original tach with the latest (both wires removed from the old sender and
one of these to "w" on the alternator, the hour meter wire removed and
set
aside, etc.). I just started up the engine for the upcoming season and
the
new tach is fine. However now I have a new issue with the temp gauge.
Here
are the symptoms.

Prior to starting, when I turn the key one click, all gauges including
the
temp move a bit, indicating that the wiring is fine to all instruments.
Nothing happens with the tach of course. When I then start up, all gauges
including the new tach perform as designed, except that the old temp
gauge
(which ran perfectly last year) pegs to the left once the engine starts,
giving what looks like reverse polarity connection symptoms. I did not
change any wiring to this gauge when fitting the new tach.

Next, when I shut down after running the engine under load and letting it
come to temp, all the gauges including the temp show what appear to be
correct readings, but only when the engine is NOT actually running.
That is,
it seems the temp sender is OK and sending correct info, the oil sender
same, the voltage meter same, the tack off of course, etc. I think this
means the temp sender is fine, but that running the engine is somehow
sending the incorrect voltage to the meter. Only when I start up and the
engine is actually running (and the tach showing the revs) does the temp
gauge peg to the left. Is it possible I just picked the wrong one of
the 2
old tach wires for the new tach to connect to "w"? No other wiring
changed
from the time the temp gauge was OK. Ideas welcomed.


Check for voltage drops between various earth points when the alternator
is charging.

In particular, check the integrity of the alternator earth path (since
it seems that the error is associated with charging current), the engine
earth path (since, probably, the temperature sensor thermistor uses the
engine as earth), and the instrument earth (since that is where you see
the problem). In an ideal world one would have a single point earth but
this is not always practical.

I'm a bit confused. Assuming a normal inboard engine installation, the
alternator earth is normally either through the case to the engine
block or through a separate earth connection to the same place. The
engine is normally grounded/earthed by a direct connection back to the
negative side of the battery.

It almost has to be connected this way as the starter, which IS
earthed through its case to the engine block will never develop its
normal power without an adequate earth/ground path back to the power
source; the battery.

Cheers,

Bruce
(bruceinbangkokatgmaildotcom)