I'm sure if you have owned a Cruiser for more than one day you
have wondered about that Amp gauge in the gauge cluster. If all is well in your
electrical system, it doesn't appear to do much of anything. The needle sits
in the middle of the -30 | 30+ range, maybe moving toward the minus side a bit
when you turn on the headlights or heater fan. Only when something is pulling
a lot of current does it deflect toward the minus side enough to notice. If
the battery gets really discharged, it will deflect toward the positive side
indicating the alternator is now sending a charge current to the battery.
How it works
The amp meter actually sits in SERIES between
the battery and the +B charge wire from the alternator. The alternator is in
parallel with the fuse box. What this means is the gauge can indicate current
going to the battery and fuse panel (needle moves toward the positive side of
gauge) or can indicate current being pulled from the battery (needle moves toward
the negative side of gauge).
The Dark Side of the Gauge...
It won't be long before you discover the dark side of having
an amp gauge. Toyota engineers are still laughing about this one...
If you look at a schematic you will see that a 10ga solid white
wire brings a direct connection to the battery inside the cab to the back of
the amp gauge. What's so remarkable about that you wonder? Well... On the day
you decide to pull the gauge cluster out to work on the speedo cable or upgrade
the gauge lights you will discover why I call this the Dark Side of the gauge.
You remove the two gauge screws and start to tilt the gauge out of the opening
SNAP! CRACKLE! POP! Smoke and sparks
start pouring out of the opening! This ALWAYS catches you totally by surprise...
If you are lucky you will only create a few sparks as the battery tries to weld
the amp gauge connecting studs to the dash. If you are unlucky, it succeeded,
and proceeded to catch the wiring harness on fire as the 10ga wires melted into
molten copper between the starter and the amp gauge!
So what caused this pyrotechnics display? The charge circuit
is one of only two circuits on the early Cruiser that are NOT
fused! (The other is the ignition wire to the coil.) So when the
Amp Meter stud contacted the metal body, it was a dead short from battery +
to ground through the 10ga white wire! Starting in 10/1971 Toyota added a fusible
link to the charge wire to prevent a major meltdown.
ALWAYS, and I mean ALWAYS, DISCONNECT THE
BATTERY before working on the gauge cluster.
Note: The Alternator was NOT intended to charge a fully discharged
battery, but to maintain a battery in a charged state! If you know the battery
is weak it's best to charge it with an external charger instead of the alternator.