Max
Seems this is a very common situation.....not really a problem. Here's
some quotes I've saved on the subject.
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Why does the alternator light stay dimly lit?
Cut the brown wire going to the idiot lamp. Insert a 25 cent Radio Shack
diode in the line in any direction. Turn on the ignition to test. If the
light comes on, you're done, just start the coach and watch the light go
out. If the lamp does not come on with the ignition, reverse the diode
(end for end) and you're done. Get a Radio Shack part number 276-1102 or
similar. (John Dolan)
GMC Tech Bullitin
"Technical Service has received several reports of the generator telltale
light glowing dimly at all times. This condition can exist even though the
alternator is operating correctly. It may be caused by a partially
discharged vehicle battery or by the small voltage drop across the dual diode
isolator.
If the above condition is encountered and the owner of the vehicle
expresses concern over it, the following procedure should be followed to
assure that it is not being caused by a malfunctioning alternator. The
owner should then be assured that the condition is normal and will not
cause any trouble in the system.
1. Disconnect the battery ground cable.
2. Connect an ammeter in the circuit at the "BAT" terminal of the alternator.
3. Reconnect the battery ground cable.
4. Turn on radio, lights high beam, and blower motor high speed. Connect
a carbon pile across the battery. {Emery's note: this is to put
more load on the battery. Try turning on a lot of 12 volt appliances in
the GMC if you don't have a carbon pile}.
5. Operate the engine at a moderate speed as required, and adjust the
carbon pile as required to obtain a maximum current output.
6. If ampere output is within 10% of rated output (80 amps) alternator is
not defective." (Emery Stora)
There is one other condition that can cause the symptom of a dimly lit
idiot lamp. A GMCer replaced his alternator, and still had the dim glow
problem. He checked a diode that is supposed to eliminate this on some
production models. NO luck. He then discovered that his 10 AMP dash
instrument gauge fuse was blown. The fuse provides 12 volts to one side of
that lamp and if it is blown it does not have 12 volts there. When the
alternator starts putting out 15 volts there is a differential 15 - 0 and
it gets an indication. Replace the fuse (or check wiring and grounds to
make sure you have 11.5 to 12 volts at the lamp and the glow should cease,
except when the alternator is not putting out 15 volts, which is the way it
is supposed to work. It was reported in GMCMN in March 98 page 5. (John
Dolan)
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Hope this helps
>Experiencing an glowing alternator light when the engine is running
>while amp meter is posting fluctuations of between 12.1 and 13.2.
>Checked belt and it's tight. Anyone had this experience? Does this
>appear to be the beginning of an alternator problem or something else?
>
>Max
>1976 Palm Beach
>
>
bdub
'76 Palm Beach
In The Heart o Texas
www.web-access.net/~bmassey/
icq # 202333
