Alternator and electrical headaches.
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Alternator and electrical headaches.
1987 Camaro 305 TPI
So the other day I noticed that electrical hum coming from my alternator with the key off. Its charging weak at or just below 13v. My guess was a diode or internal part went bad inside the alternator. But after some poking around and looking at wiring diagrams, there seems to be confusion as to what wire is the exciter for the alternator. Most sources say the brown wire is the excitor wire. At my alternator i have:
batt+ voltage at the large terminal.
Batt+ at the red “S” wire.
Batt+ at the brown/white “F” wire
nothing at the brown “L” wire.
To my understanding i should have nothing at the brown/ white and ign switched resisted voltage at the brown wire.
And to add to the confusion, some things have power supplied all the time that i believe should not. My power windows mirrors, hvac blower will work with the key removed. Havnt had much luck finding power distribution info but could this be ign switch related?
Gauges/dash lights/ fuel pump seem to cycle normally with key. Anybody have any input before i put in a new alternator?
So the other day I noticed that electrical hum coming from my alternator with the key off. Its charging weak at or just below 13v. My guess was a diode or internal part went bad inside the alternator. But after some poking around and looking at wiring diagrams, there seems to be confusion as to what wire is the exciter for the alternator. Most sources say the brown wire is the excitor wire. At my alternator i have:
batt+ voltage at the large terminal.
Batt+ at the red “S” wire.
Batt+ at the brown/white “F” wire
nothing at the brown “L” wire.
To my understanding i should have nothing at the brown/ white and ign switched resisted voltage at the brown wire.
And to add to the confusion, some things have power supplied all the time that i believe should not. My power windows mirrors, hvac blower will work with the key removed. Havnt had much luck finding power distribution info but could this be ign switch related?
Gauges/dash lights/ fuel pump seem to cycle normally with key. Anybody have any input before i put in a new alternator?
Last edited by Blue Pearl; Aug 31, 2018 at 11:46 AM. Reason: Additional info
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Re: Alternator and electrical headaches.
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Re: Alternator and electrical headaches.
The wires that connect to my alt are red, brown, and brown/white. And of course the main red wire from the post to the batt. I’m seeing different responses as to what each wire’s function should be.
Joined: Mar 2001
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Car: '89 Firebird
Engine: 7.0L
Transmission: T56
Re: Alternator and electrical headaches.
I'm not familiar with your alternator, but usually,
S terminal (Sense) is used as a voltage reference for the voltage regulator. The alternator will keep charging until it sees proper voltage at that sense terminal. If nothing is connected to the S terminal then the alternator will reference its own internal voltage instead. Alternator should work whether or not anything is connected to the S terminal.
L terminal (Lamp) is used to turn a light bulb on and off as a charging indicator. It is not needed for the alternator to function.
F terminal (Field) is the excitation wire. It must be connected for alternators that require external excitation. It does not need to be connected for alternators with internal excitation. I do not know the specifications for your alternator.
The I terminal is like an F and L terminal combined into one. It needs a resistor on the external wire to lower current draw, otherwise the alternator will be damaged.
S terminal (Sense) is used as a voltage reference for the voltage regulator. The alternator will keep charging until it sees proper voltage at that sense terminal. If nothing is connected to the S terminal then the alternator will reference its own internal voltage instead. Alternator should work whether or not anything is connected to the S terminal.
L terminal (Lamp) is used to turn a light bulb on and off as a charging indicator. It is not needed for the alternator to function.
F terminal (Field) is the excitation wire. It must be connected for alternators that require external excitation. It does not need to be connected for alternators with internal excitation. I do not know the specifications for your alternator.
The I terminal is like an F and L terminal combined into one. It needs a resistor on the external wire to lower current draw, otherwise the alternator will be damaged.
Thread Starter
Junior Member
Joined: Nov 2016
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Re: Alternator and electrical headaches.
I'm not familiar with your alternator, but usually,
S terminal (Sense) is used as a voltage reference for the voltage regulator. The alternator will keep charging until it sees proper voltage at that sense terminal. If nothing is connected to the S terminal then the alternator will reference its own internal voltage instead. Alternator should work whether or not anything is connected to the S terminal.
L terminal (Lamp) is used to turn a light bulb on and off as a charging indicator. It is not needed for the alternator to function.
F terminal (Field) is the excitation wire. It must be connected for alternators that require external excitation. It does not need to be connected for alternators with internal excitation. I do not know the specifications for your alternator.
The I terminal is like an F and L terminal combined into one. It needs a resistor on the external wire to lower current draw, otherwise the alternator will be damaged.
S terminal (Sense) is used as a voltage reference for the voltage regulator. The alternator will keep charging until it sees proper voltage at that sense terminal. If nothing is connected to the S terminal then the alternator will reference its own internal voltage instead. Alternator should work whether or not anything is connected to the S terminal.
L terminal (Lamp) is used to turn a light bulb on and off as a charging indicator. It is not needed for the alternator to function.
F terminal (Field) is the excitation wire. It must be connected for alternators that require external excitation. It does not need to be connected for alternators with internal excitation. I do not know the specifications for your alternator.
The I terminal is like an F and L terminal combined into one. It needs a resistor on the external wire to lower current draw, otherwise the alternator will be damaged.
And maybe the hum is there because the alt is being “excited” at all times when it should only be while the key is on. Any clues as to how that could happen?
.. i’ll try and put more info about the alt later, but i know it’s a reman with the 3 wire connector.
Joined: Mar 2001
Posts: 10,415
Likes: 2,083
Car: '89 Firebird
Engine: 7.0L
Transmission: T56
Re: Alternator and electrical headaches.
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