Comment below:
"Jeff" wrote in message
...
Larry W4CSC wrote:
Jeff wrote in :

chunks of stuff snipped for brevity

Ken mentioned that the voltage drop could affect the gauges. I can
see how the cheap fuel gauge might have a problem but it made me
wonder if the water temp gauges would be affected. Not that I would
need the diodes for them, but the alternator output can vary from 12
something (turned off) to 14.5, depending on what's going on in the
regulator's little mind. I have to believe that such fluctuations
don't make much of a difference in the temp readout, but I couldn't
find a spec on the Teleflex site that indicated they were stable over
a reasonable voltage range. Any thoughts?

I haven't seen a schematic for boat instrument systems but will make a
comment on how automotive instrument systems used to work. (They may still
work this way, but I haven't been around this stuff for years) Automotive
instrument systems (used to) receive their 12 V. + feed from a simple
voltage regulator mounted in the dashboard wiring system. This prevented
the varying voltage coming from the alternator from causing erratic readings
on the instruments. Automotive gauges at the time were thermal in operation
(because they were much cheaper to build that way), and so were sensitive to
voltage variation. You could tell good instruments (usually aftermarket)
from these thermal types when you turned the ignition switch on. Good ones
would snap to the indicated reading, the thermal ones would take a few
seconds to rise up to the correct indication. Gas gauges would often not
give a true reading of tank level until you started the motor and the
alternator kicked in. Again, I'm not sure if boat gauges are wired this
way.
--
Ken Heaton, Cape Breton Island, Canada
kenheaton AT ess wye dee DOT eastlink DOT ca

"Ken Heaton" wrote in
news:J3Mle.13142$HI.6104@edtnps84:

Gas gauges would often not
give a true reading of tank level until you started the motor and the
alternator kicked in. Again, I'm not sure if boat gauges are wired this
way.


Of course, we all know how DEAD ACCURATE those wonderful BOAT gas guages
monitor the fuel supply that can strand you miles from nowhere.

When my Sea Ray read 1/2 full, it meant you used 6.5 of the 25 gallon tank.
When it read empty, you had used 9.5 gallons of the 25 gallon tank. When
it read below empty, you simply opened the "trunk" and leaned down into the
bilge so you could see the fuel level in the stern end of the cheap
polyethelene tank supported by two little plastic brackets digging into the
milk jug material 25 gallons of fuel were waiting in to blow you all to
hell if it leaked. It's nice-looking Sea Ray gas guage was damned near
useless....

The tach seemed to work....