I found a new problem with my '99 XLT 4x4 Expy w/ 80,000 miles on the dial while on my way home tonight, when the engine reaches revs of approx. 3250+ rpms the battery light flickers/flashes. I noticed that while the battery light was flickering, the battery/voltage gauge was leaning slightly off dead center towards a high charge. As soon as I noticed this, I changed destinations to Auto Zone about a mile and a half away thinking I might have to replace the battery, which as far as I can tell hasn't been replaced ever. I explained the problem to them and they tested the battery and it was reading 12.8 or so on their voltimeter. My question is, have any of you out there heard of an alternator over charging? From everything that I've ever heard, alternators were more prone to under charge and die than over charge. Thanks in advance for your help.

Smitty

 

Per my manual:
With the ignition switch in the RUN position, voltage is applied through the warning indicator I circuit 904 (LG/RD) to the voltage regulator. This turns the regulator on, allowing current to flow from battery sense A circuit 35 (OG/LB) to the generator field coil. When the engine is started, the generator begins to generate alternating current (AC) which is internally converted to direct current (DC). This current is then supplied to the vehicle's electrical system through the output (B+) terminal of the generator.

Once the generator begins generating current, a voltage signal is taken from the generator stator and fed back to the regulator S circuit 4 (WH/BK). This voltage feedback signal (typically half the battery voltage) is used to turn off the warning indicator.

With the system functioning normally, the generator output current is determined by the voltage of the A circuit 35 (OG/LB). The A circuit 35 (OG/LB) voltage is compared to a set voltage internal to the regulator, and the regulator controls the generator field current to maintain the correct generator output.

The set voltage will vary with temperature and is typically higher in cold temperatures and lower in warm temperatures. This allows for better battery recharge in the winter and reduces the chance of overcharging in the summer.


Battery Positive Output (B+) Circuit 38 (BK/OG)

The generator output is supplied through the battery positive output (B+) terminal on the back of the generator to the battery and electrical system.

I Circuit 904 (LG/RD)

The I (ignition) circuit 904 (LG/RD) is used to turn on the voltage regulator. This circuit is powered up with the ignition switch in the RUN position. This circuit is also used to turn the charging system warning indicator on if there is a fault in the charging system operation.


A Circuit 35 (OG/LB)

The A (battery sense) circuit 35 (OG/LB) is used to sense battery voltage. This voltage is used by the regulator to determine generator output. This circuit is used to supply current to the generator field (rotor). The amount of current supplied to the rotor will determine generator output.


S Circuit 4 (WH/BK)

The S (stator) circuit 4 (WH/BK) is used to feed back a voltage signal from the generator to the regulator. This voltage is used by the regulator to turn off the charging system warning indicator. The S circuit is fed back externally on external mounted regulator generators.


IF THE CHARGING SYSTEM WARNING INDICATOR FLICKERS OR IS INTERMITTENT

A. CHECK FOR LOOSE CONNECTIONS
B. CHECK FUSE CONNECTIONS
C. CHECK A CIRCUIT 35 (OG/LB) CONNECTIONS
D. INSPECT GENERATOR S TERMINAL C177
E. CHECK GENERATOR BRUSHES
F. CHECK FOR A GROUNDED SLIP RING

Hope this helps.