# need help!!!!!!



## POSentra (Feb 12, 2010)

1998 nissan sentra.. new alt, batt. and batt. terminals. car will start when jump but dies within 10 mins. while driving (if i have a full charge from the parts store and it starts) the headlighs at night go out but my parking lights stay on guage cluster dims, and then air bag light flashes then when that happens if i am on the gas car slows like on the brakes then when shuts off wont start back up


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## chimmike (Oct 17, 2002)

here's what I think is happening.
Alternator belt is off or lose, alternator can't charge battery, battery dies while driving. Recharges fine at the auto parts store, but the same thing happens.

or the alternator is fcked, either way, the battery isn't getting charged and the car is running off the battery alone, killing it quick and the car dies.


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## POSentra (Feb 12, 2010)

had the alt checked before purchase, belts are tight.


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## chimmike (Oct 17, 2002)

then the wiring connection between the alternator and the battery isn't right. Something electrically is preventing the alternator from charging the battery and keeping the car running.

that's my guess.


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## POSentra (Feb 12, 2010)

yea ill check that out when i get home today i hope thats it but does the alternator not charging the battery justify the on the gas slowing down??


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## chimmike (Oct 17, 2002)

well that's because there's no power going to the spark plugs. listen. the entire car running off battery, the battery drains down to nothing, lights will dim, stereo gets quieter, etc, and the car will act the same way and die.


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## nova73guy (Mar 30, 2004)

Car slowing down is due to lack of power going to: fuel pump, ecu, injectors, ignition coil, etc. Also (just a side thought), constantly running the battery down can damage the ecu and other modules in the car.

From what you're saying it sounds like you replaced the terminals on the battery cables instead of the entire cable, correct? If so, make sure you got all of the cables reconnected to the battery, and that the connection inside the terminals is clean and tight. If the alternator tests good, it may be that the ground cable isn't making sufficient contact at the battery.

Only other thing is the circuit that comes from the ignition switch and energizes the alternator. If that's not working, the alternator won't charge. make sure it's plugged in, and use a test light to determine if it's getting power when the ignition switch is on.


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## IanH (Feb 11, 2003)

x2

To check put a cheap digital multimeter on 20V range and measure your battery voltage with the car off.

then start the car. Voltage should be at least 1 -2 volts higher, if not its not charging !!!

Battery fully charged engine off should be 12.5 - 13.2 volts.

Reading with a fully charged battery with engine running should be about 14 V.


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## POSentra (Feb 12, 2010)

where can i buy wiring for the alt and all wires have power from the alt excepy the clip that has the 3 smaller wires any sugestions


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## IanH (Feb 11, 2003)

I think you need to slow down.

Look at this ..










Check all the fuses on the diagram first

check the voltages I gave above


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## IanH (Feb 11, 2003)

Then if you can confirm the fuses are good and the Alt isn't charging you can probe the wires for voltage. Yellow / Red and Red /black.


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## POSentra (Feb 12, 2010)

ok im 19 ive rebuilt and built motors this is my 1st wiring task so im not really sure on how to read that?????? sorry just gotta ask questions to learn


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## IanH (Feb 11, 2003)

Thats OK we have all started somewhere.

Do you have a cheap digital multimeter ?

there are very reasonable these days, $2.99 on sale at Harbor freight, under $10 most places.

If you pay over $20 it better be special !!! Make sure you get one with 20V DC range.

What the diagram is telling you is that there are two voltage feeds needed to make the alternator "go" and one warning light circuit.

The alternator used on cars uses 12V from the battery to power the rotor and stator.
This is different from a Dynamo or Alternator with fixed magnets.
The magnetic field is current generated.

The Alternator has brushes on two slip rings to power the rotor.

Inside the Alternator is a voltage regulator. This stops the Alternator from overcharging the battery and killing it.

There is no Current limiter, Alternators are self current limiting ( Old style dynamos arent !!) 

the lead marked W is the main power to the battery lead, and goes to the ring terminal.

this has the 75 Amp fusible link.

Check the fuses.

Measure the voltages.

The alternator also has a power diode stack inside and sometimes a diode trio to sense voltages difference for the warning circuit, but for now we are not worried about these.


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## IanH (Feb 11, 2003)

the lead marked R/B Red / Black stripe is the power supply for the rotor and stator. 
You must have 12V here or it wont work. Note that there is no switch or control here, its always on unless the fuse or the fusible link is blown


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## IanH (Feb 11, 2003)

Does your battery light light up when you turn on the ignition ?
If so the fuse is good.
When its running what warning lights are on ???


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## POSentra (Feb 12, 2010)

Holy shit my friend who is a mechanic was the one who help with the alt he didnt plug the damn plug into the alt so thats what it was wasnt it?


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## IanH (Feb 11, 2003)

yes !!! Thats it


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## POSentra (Feb 12, 2010)

thank you i feel dumb for not checking something so small:lame:


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