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1995 Chevrolet Silverado:
Battery Discharge, New Alternator

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Alex Steele
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Question:

 

My 1995 Chevy Silverado (2500, 5.7-liter engine, and a 100 amp alternator) has recently been discharging the battery as I drive. I replaced the battery and the alternator, but the problem persists.

 

I checked thoroughly for wires touching the block, but could find nothing. The blinkers, heater, etc. seem to work okay, but the charge gage continues to go down until the truck finally shuts off.

 

Answer:

 

Quality varies depending on where you bought the alternator and what you paid for it, so let's keep the possibility of a defective replacement part in the back of our minds.

 

In the meantime, turn the ignition on and look for the generator light on the instrument cluster. Even though you have a volt gauge you still have an idiot light. If the charging system is functioning correctly the indicator will light up with the ignition on, and go out when the engine is running. If it doesn't light up at all, check fuse #4 in the fuse block on the lower left-hand side of the instrument panel. If the fuse and indicator bulb are good, then we're looking for a break somewhere in that circuit, or a bad alternator.

 

This alternator is externally simple with an internal voltage regulator doing the electronic tough-stuff. But we have to keep it cleanly bolted to the engine to provide a good ground, the circuit form the alternator to the generator light has to be working (brown wire, terminal "L" at the 4-terminal alternator connector), and there has got to be a complete high amperage circuit (heavy gauge black and red wire) from the alternator output terminal to the positive side of the battery.

 

A quick way to confirm the alternator's connection to the battery is to remove the output wire from the alternator and check it with a 12-volt test light. If it lights up, you're good, if it doesn't, follow that circuit to the battery and find the break. A likely trouble-spot will be the blue fusible link located closer to the battery. The fusible link is a wider section of the alternator output wire with an internal element which burns through under excessively high amperage conditions (like a regular fuse). Sometimes the outside of a link will look good, but the element is still burnt through beneath the insulation. Pull on either side of the fusible link. If it stretches, it's no good.

 

After that, be sure the alternator output circuit has a good connection all the way to the positive battery terminal, both terminals are clean and tight, and the negative side of the battery has solid connections to both the engine and the chassis.

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Comments:

Joe calderon
20 Apr 2018, 20:27
Your problem it may be a bad generator..I had the same issue with a 1995 g30..i got a alternator at advance auto parts.it was defective,took it back to get it check they told it was good...took same alternator to auto zone they check it..it was bad...so people from advance lie .bought alternator.at auto zone..samething ,same problem..took alternator back to auto zone they check it..was bad..they gave another one.but this time I did not leave store till they check new one..and no problems no more
TechHelp2
06 Apr 2016, 11:32
RE: Leo Bowen, I would like to know the voltage at the battery when the truck is running and also how many amps the alternator is putting out.

A regular charging rate is about 14.2 volts. If the amperage is high the voltage will be lower until the battery is fully charged. That is typical OHM's Law, low amps high voltage high amps low voltage.

Check all fuses; check the battery cables making sure they are clean and tight. Check the cables for any crack or corrosion which can lead to high resistance which can affect the charging rate. Also check the ground wire and the body grounds for corrosion or loose connection.

The battery should also be checked by a load test to see if it is within specs.

Remember that there is also a possibility that the alternator could be faulty even though it is a rebuilt replacement.

Get back to me with your results, we can diagnosis the problem further if needed.
Leo Bowen
06 Apr 2016, 07:34
My truck starts up and runs, the alternator gauge reads Low on the Red Line and the battery light goes off when the truck starts. What would be the problem? I have a brand new alternator.

 

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