Battery current drain solved


Ken Chambers

Hi all,

Seems that some Amphicars have an annoying problem where a current drain
depletes the battery within a week or so. I believe the factory fixed the
problem at some point. There's a poll at the end of this report to try to
identify at which serial number the factory solved the problem.

My '64 Amphicar, s/n 100320, certainly has the problem. After a week or two,
the battery is deader than a door nail. To make a long story short, the problem
lies with how the engine temperature gauge is connected to the car's wiring.
The way the gauge is wired on my car is a wire from the #30 (always hot)
terminal of the ignition switch goes to a terminal on the temperature gauge. A
wire connects the other terminal of the gauge to the engine temperature sensor
which then goes to
ground, completing the circuit. The wiring on my car is all original and the
owners manual wiring diagram confirms that this is the way the factory wired it.

The only reason I can think of as to why the factory chose to wire the gauge
always on was to get the gauge to read "cold" when the engine is off. In other
words, with nothing connected to the temperature gauge it pegs to "hot". It
requires electrical current to get it to read cold when the engine is cold.

I measure 200mA (0.2Amps) of current draw across the gauge. My fairly new Delco
Marine/RV battery claims to have 620 Marine Cranking Amps (whatever they mean by
that). It also says 400 CCA (cold cranking amps). This means how many amps
their laboratory controlled cold (doesn't say how cold) battery will supply for
some short duration of time. Remember, what's printed on the battery is as good
as it gets. Your mileage will vary. There's also an interesting little chart
printed on
top of the battery that's a much truer representation of the battery
performance. Delco's legal department probably put it there to provide people a
little more information to avoid getting stranded in the middle of the lake
while powering their trolling motor.

Performance chart on this Delco battery:
Hrs Amps
14.4 5.0
4.0 15.0
2.1 25.0

By multiplying across you'll arrive at Amp-hours. That's what a NEW battery, in
a fully charged condition, is supposed to deliver. The smaller the current
draw, the higher the Amp-hrs, to a point. This battery is advertised as a 80
Amp-hour battery, which computes with the above chart at light loads.

So, in doing the math, 80 Amp-hours / 0.2 Amps = 400 hours, or about 16 days to
a really dead battery.

(BTW, and FWIW, I came across an article recently that published the results of
a non-scientific poll taken among motor heads as to which brand of battery they
liked best. It took into consideration a number of factors like, cost,
longevity, performance, and acid leakage. Delco came out on top. That
motivated me to use that brand.)

So the fix is to move the wire from the #30 terminal on the ignition switch to
the #15/54 ignition switch terminal. In doing so will cause the gauge to read
full hot with the ignition switch off. Upon starting the engine, the gauge will
move to cold, then track engine temperature normally as the engine heats up.
Perhaps a better place to rewire the gauge is to work entirely behind the
cluster gauge. After removing the wire from the number 30 terminal of the
ignition switch, pull it
back to the cluster gauge and connect it to the wires that are common to the
fuel gauge, ammeter light and oil pressure lamp. Looking at a later model
wiring diagram, that's the way the factory later wired it.

Now here's the poll: Which cars do - and do not - have the battery current
drain problem? Guess that includes everyone. That will certainly give a lot
more data points. Too bad some cars are put away for the season. Please state
whether or not your temp gauge pegs full hot or cold when off - and the chassis
serial number.

It will be interesting to see if we can narrow down to what s/n the wiring was

Best regards,
Ken Chambers, CA
'64 Amphi, 100320


My 1964 Amphicar #100337 also had the temperature gauge hooked up to the
"always hot" terminal on the ignition switch. I fixed it exactly as you did.

John Davis
Tulsa, OK

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