Charging System Light; Voltmeter Gage - GMC 2003 GMT560 T-Series Owner's Manual

Charging System Light

It should come on briefly when you turn on the ignition,
before the engine is running, as a check to show
that it is working.
If it stays on, or comes on while you are driving, have it
checked right away. You could have a loose generator
drive belt or some other problem.
Driving while this light is on will drain your battery. If you
must drive a short distance with the light on, turn off
your radio and other accessories. Sustained driving with
a generator failure could result in a lack of back-up
braking if the engine quits or the power steering pump
should fail.
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The charging system
indicator light may be
located in the instrument
panel cluster, or with
the auxiliary warning lights
in the center of the
instrument panel.

Voltmeter Gage

Readings in either warning zone indicate a possible
problem in the electrical system.
Readings in the low warning zone may occur when a
large number of electrical accessories are operating in
the vehicle and the engine is left at an idle for an
extended period. This condition is normal since the
charging system may not be able to provide full power
at engine idle. As engine speeds are increased, this
condition should correct itself because higher engine
speeds allow the charging system to create
maximum power.
You can only drive a short time on the battery. Be sure
to shut off the radio, the fan or any unnecessary
accessories and have the system serviced.
When your engine is
running, the voltmeter
gage, at the right side of
the instrument panel
cluster, shows the charging
system voltage.