1991 Lexus LS 400 Logo

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Posted on May 10, 2011
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Alternator not charging, exchanged with known good one still not charging, checked fuses

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Hashim Khan

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  • Expert 148 Answers
  • Posted on May 10, 2011
Hashim Khan
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Joined: May 03, 2011
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When you swapped the alternator, did you also changed the alternator rectifier? Looks like its either rectifier problem or problem with battery itself. Try using battery from another car and see if its charging. This will be the easiest troubleshoot for now. If still not charging then use a multimeter to check the output of alternator.

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0helpful
4answers

Put new alternator and 2 new batteries, you can drive the vehicle down the road and it running fine and it looses all electrical power like the battery is completely dead, Jump start it and its like...

It sounds as if the vehicle is running on the battery power only. Check the battery voltage at the battery when the vehicle is off completely. Record that value. Now, start the vehicle and check the voltage at the battery the same way. If the voltage is NOT at least 1-1.5 volts higher, the battery is not being charged. If this should be the case, you have to check the alternator and all the wiring and their values that are connected to it. A good auto electrician can tell you the fix with little diagnosis.
tip

Automobile battery and charging system


Most automobile batteries are lead acid which should have a standing voltage of about 12.6V fully charged at 70 degrees F. To test a battery first it must be fully charged. If fully charged a good battery will stay above 9.5V while cranking engine. Most part stores will charge and test batteries, starters and alternators. To be sure your alternator is properly charging start the engine and turn on the headlights and blower fan to add electrical load. Voltage should be over 13.2V at idle and under 15V with a known good battery. If not check the larger wire bolted to the back of the alternator for loose connection and continuity to the battery. If ok check fuses. If all are present and check good most likely the alternator is bad and needs replacement, although it is possible on many modern automobiles to have a powertrain control module (PCM) be the problem as they serve as the voltage regulator. Most late 90s and newer GM and Chrysler do. If all else fails have a professional check it to be sure. Hopefully this will answer the questions of many. Good luck ??.

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on Feb 01, 2015 • Cars & Trucks
0helpful
5answers

Battery not charging

Check your wire connections make sure they are tight. But it sounds as though your alternater is bad and not charging your battery. A local parts house can test it for you.
0helpful
1answer

Charging system

Hi William
to start with, check if there is output voltage from the alternator it self ( at the back of the alternator ) using a voltmetre
Chould give 14.0 Volt, if is OK, that means you have a broken wire between the alternator and the battery, this is common.
good luck
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1998 isuzu trooper need wiring diagram for charging system with a3.5 li5ter motor

1998 trooper new alternator and still not charging and alternator bench tested good,
Check main 80 amp fuse in engine compartment and also check fuses in inside fuse box, there two in that one. first is engine fuse 15amp and the 10amp gauge fuse,

Here is the wiring diagram for the charging system as you asked for , also check connections, follow battery wire off the back of alternator make sure connections are good , that wire runs to engine fuse box and that is one fuse that i said to check it is 80amp, hope this is helpful good day9_30_2012_10_15_05_pm.gif
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I have a weird symbol showing on the dash for my 1985 blazer that I don't know what it means. I am having a problem starting it without a jump and then it doesn't want to stay charged. New battery, plugs,...

ok get power to truck turn key to on position pull plug off altenater one of then should be hot its call an exciter wire to excit the altenater to starg charging but first before all that check the alt. fuse inside your truck
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I have a 98 jeep grand cherokee limited v8 and the battery keeps draining when the vehicle is off. It'll start fine after being jumped so we let it run to charge the battery back up for about half an hour...

MAKE SURE BATTERY CABLES IS CLEAN FREE FROM CORROSSION. MAKE SURE BATTERY CABLES GOOD TIGHT.IF ALL IS OKAY. WELL I HAVE SEEN A GOOD BATTERY CAN ALSO BE BAD.I KNOWN PERSON BOUGHT NEW BATTERY DIDNT LAST A WEEK.IT HAD A FACTORY DEFECT ALTERNATOR WAS GOOD.DO A QUICK CHECK TO SEE IF ALTERNATOR CHARGING BATTERY.CRANK VECHICLE UP CHECK VOLTAGE OUT PUT AT BATTERY.IT SHOULD BE 13.5 - 14.5 VOLTS.IF NOT ALTERNATOR NOT WORKING CHECK ALTERNATOR FUSE AND WIRES.MAKE SURE THEY ARE INTACT.IF ALTERNATOR GOOD.HAVE THE BATTERY LOAD TEST TO SEE IF YOU HAVE A BAD CELL IN IT.IF BATTERY IS GOOD.BATTERY DRAIN CAN BE CAUSED BY RADIO STAYING ON.THE INTERIOR LAMP STAYS ON.FAULTY PCM SHORTING OUT.FAULTY DOOR LOCK SWITCH.FAULTY BLOWER MOTOR RELAY.FAULTY ALTERNATOR DIODE.FAULTY STARTER SOLENOID SHORTING CONTACTS WILL DRAIN BATERY.
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Is there a fuse in car or under hood that would stop the battery charging system fro working in 98 lincoln town car

yes there is a fuse, labeled alt fuse and its under the hood in the relay fusebox, if the car is not charging, then just check for power to the alternator, the small wire not the big one, good luck,
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REPLACED THE ALTERNATOR BUT THE BATTERY WILL NOT CHARGE

In this year , there may be an external VOLTAGE
REGULATOR .Instead of an internal regulator inside the alternator. It is usually a square box to the passenger side attached to the fender inside wall. Try replacing this box with a known good one. Or new one if you can get it right away.
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My battery went flat, so I charged it and started the vehicle and noticed that it was only charging at 10 volts, I fitted a new alternator, and the battery now charges at 13.8 volts. however if I switch...

check all of your engine block grounds and positve leads, sounds like the regulator is working also check your main alernator fuse please rate -jeff
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