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Old 10-20-2019, 12:05 PM   #11
fdryer
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Join Date: Jan 2006
Location: NYC
Posts: 43,261
 

2003 L-Series 3.0L Sedan
Default Re: Battery Dead. Jumped car and it died while driving

From descriptions, your wiring seems correct. The small purple wire occupies the small terminal on the starter solenoid, the two larger gauge wires on the outside starter terminal. The large gauge battery cable supplies battery voltage, the second wire supplies power to the alternator as an extension wire from the battery cable. This wire is a fusible link wire. The whole length of this wire is designed to carry no more than 25 amps to protect against a short in the alternator from damaging the battery. The alternator case is ground thru the engine block with a negative cable going back to a chassis stud then back to battery negative. If the fusible link wire is damaged or broken, power to the alternator won't show the alternator to operate. The car is running solely on battery power and killing it. The alternator supplies all the power to the car's electrical system white show charging the battery after every start. The battery is only used to power the starter and run accessories if the engine isn't running. Once the engine runs, the alternator takes over and generates around 14.5v. Not seeing 13 or 14 volts indicates either the fusible link wire is broken or the alternator is faulty. There's an easy test to determine which one failed.

Crawl under the car and measure the side terminal of the alternator. This the the other end of the fusible link wire from the starter. Measured against alternator case ground, you should see battery voltage. If you do not see battery voltage on the alternator side terminal, the fusible link wire is damaged and needs to be replaced. The alternator is always supplied battery power and doesn't drain the battery due to internal electronics. It only draws power when the engine's running. If you have battery power on this side terminal, the alternator is dead. If this is the case, remove and replace it. You can have the alternator tested at AutoZone or any auto store providing free battery and alternator testing.

A faulty fusible link wire or alternator will not supply power to the car. The battery is doing all the work when its main role is to power the starter. The alternator takes over after the engine runs to supply all the power to the car's electrical system while simultaneously recharging the battery.

Last edited by fdryer; 10-20-2019 at 12:12 PM..

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