98 LS1 Wiring Harness - Alternator Exciter wire what should the voltage be.
04-09-2011, 06:39 PM
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98 LS1 Wiring Harness - Alternator Exciter wire what should the voltage be. I have a LS1 in a Mazda FC with custom chassis Harness with 1998 LS1 engine harness.
I have researched this topic extensively but can't find the answer I am looking for and I am not an electrical guru but I know some stuff.
I know I need to have a 470ohm 1/2 watt resistor in line with the exciter wire that plugs into the top of the alternator and that is installed, and I am sending 12v's from my accessories fuse bank unfused. I have a brand new Alternator the old one had a diode fail I guess so I just picked this one up and don't want to fry it.
The question is when I check the voltage on the exciter wire before it plugs into the alt it still has 12 volts even with 470ohm resistor. So I would like to know if anyone has a Straight up answer on what the voltage regulator in the ALT needs to see. Is it 7v is it 9v is it 10v?????? How much voltage does a 470ohm 1/2 resistor drop? I wouldn't imagine very much.
Basically can't get the car to charge, and the problem is making me disgruntled.
Please help out a newb to the forum but not wrenching.
I have researched this topic extensively but can't find the answer I am looking for and I am not an electrical guru but I know some stuff.
I know I need to have a 470ohm 1/2 watt resistor in line with the exciter wire that plugs into the top of the alternator and that is installed, and I am sending 12v's from my accessories fuse bank unfused. I have a brand new Alternator the old one had a diode fail I guess so I just picked this one up and don't want to fry it.
The question is when I check the voltage on the exciter wire before it plugs into the alt it still has 12 volts even with 470ohm resistor. So I would like to know if anyone has a Straight up answer on what the voltage regulator in the ALT needs to see. Is it 7v is it 9v is it 10v?????? How much voltage does a 470ohm 1/2 resistor drop? I wouldn't imagine very much.
Basically can't get the car to charge, and the problem is making me disgruntled.
Please help out a newb to the forum but not wrenching.
Last edited by FLKayakAngler; 04-09-2011 at 07:14 PM.
04-10-2011, 06:52 AM
#4
Here is your answer; long but informative.
The alternator needs about 8 volts on the exciter terminal to properly function. With COMPLETED circuit, the resistor will drop the 4-5 volts, down to the 8.
If you dont complete the circuit with the resistor, it will still read 12 volts. It's like measuring the voltage out of a wall outlet and again at the end of a 100 foot extension cord, it will still read the same. Another example, if you place two lights in series with a battery, each will drop half of the voltage.
On a LS1 harness, the resistor is not needed if wired like the factory. i.e. red alternator wire to PCM red connector Pin 15. The PCM will provide the voltage drop down to approx 5-8 volts. When the engine is running and you place more electrical load (current draw) on the chassis circuit, the PCM senses the lowerd voltage and tells the alternator to output more voltage to return the batteryvoltage to approx 13.4 volts.
Lastly, I do not generally use a resistor; I use an idiot lamp in series connected to switched ignition source just like the pre LT1 GM vehicles. Here is why; IF the resistor or alternator goes bad, you will not now it till your battery is so dead the car wont start or it simpy wont charge. If you use a lamp, and the alternator goes bad and stops regulating the battery voltage to 13.4 volts, the exciter terminal will be less than the battery voltage and the difference in voltage will make the lamp illuminate.
whew....got all that?
The alternator needs about 8 volts on the exciter terminal to properly function. With COMPLETED circuit, the resistor will drop the 4-5 volts, down to the 8.
If you dont complete the circuit with the resistor, it will still read 12 volts. It's like measuring the voltage out of a wall outlet and again at the end of a 100 foot extension cord, it will still read the same. Another example, if you place two lights in series with a battery, each will drop half of the voltage.
On a LS1 harness, the resistor is not needed if wired like the factory. i.e. red alternator wire to PCM red connector Pin 15. The PCM will provide the voltage drop down to approx 5-8 volts. When the engine is running and you place more electrical load (current draw) on the chassis circuit, the PCM senses the lowerd voltage and tells the alternator to output more voltage to return the batteryvoltage to approx 13.4 volts.
Lastly, I do not generally use a resistor; I use an idiot lamp in series connected to switched ignition source just like the pre LT1 GM vehicles. Here is why; IF the resistor or alternator goes bad, you will not now it till your battery is so dead the car wont start or it simpy wont charge. If you use a lamp, and the alternator goes bad and stops regulating the battery voltage to 13.4 volts, the exciter terminal will be less than the battery voltage and the difference in voltage will make the lamp illuminate.
whew....got all that?
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04-12-2011, 09:20 PM
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Here is your answer; long but informative.
The alternator needs about 8 volts on the exciter terminal to properly function. With COMPLETED circuit, the resistor will drop the 4-5 volts, down to the 8.
If you dont complete the circuit with the resistor, it will still read 12 volts. It's like measuring the voltage out of a wall outlet and again at the end of a 100 foot extension cord, it will still read the same. Another example, if you place two lights in series with a battery, each will drop half of the voltage.
On a LS1 harness, the resistor is not needed if wired like the factory. i.e. red alternator wire to PCM red connector Pin 15. The PCM will provide the voltage drop down to approx 5-8 volts. When the engine is running and you place more electrical load (current draw) on the chassis circuit, the PCM senses the lowerd voltage and tells the alternator to output more voltage to return the batteryvoltage to approx 13.4 volts.
Lastly, I do not generally use a resistor; I use an idiot lamp in series connected to switched ignition source just like the pre LT1 GM vehicles. Here is why; IF the resistor or alternator goes bad, you will not now it till your battery is so dead the car wont start or it simpy wont charge. If you use a lamp, and the alternator goes bad and stops regulating the battery voltage to 13.4 volts, the exciter terminal will be less than the battery voltage and the difference in voltage will make the lamp illuminate.
whew....got all that?
The alternator needs about 8 volts on the exciter terminal to properly function. With COMPLETED circuit, the resistor will drop the 4-5 volts, down to the 8.
If you dont complete the circuit with the resistor, it will still read 12 volts. It's like measuring the voltage out of a wall outlet and again at the end of a 100 foot extension cord, it will still read the same. Another example, if you place two lights in series with a battery, each will drop half of the voltage.
On a LS1 harness, the resistor is not needed if wired like the factory. i.e. red alternator wire to PCM red connector Pin 15. The PCM will provide the voltage drop down to approx 5-8 volts. When the engine is running and you place more electrical load (current draw) on the chassis circuit, the PCM senses the lowerd voltage and tells the alternator to output more voltage to return the batteryvoltage to approx 13.4 volts.
Lastly, I do not generally use a resistor; I use an idiot lamp in series connected to switched ignition source just like the pre LT1 GM vehicles. Here is why; IF the resistor or alternator goes bad, you will not now it till your battery is so dead the car wont start or it simpy wont charge. If you use a lamp, and the alternator goes bad and stops regulating the battery voltage to 13.4 volts, the exciter terminal will be less than the battery voltage and the difference in voltage will make the lamp illuminate.
whew....got all that?
