Great video. Glad I found it. Finally a great explanation on a 'hands on' description of the wires in the 3 wire connector and what each wire does. I will incorporate this in a bench test of an alternator I have suspected is bad sometime in the coming days. Appreciate you taking the time to make this and to post it.
Great job - I really liked how it didn't quite work out the first time but you explained what the problem likely was and sure enough it worked great by the end. Thanks!
Didnt want to kill your 4:20 likes, making it 421, but it was the most informative video I've found within last hour, trying to find the answer for my case ))
This is just the video I was looking for. When I test the voltage coming from the plug on the car, I get 5v. Is it possible that some alternator voltage regulators need 5v being supplied not 12v?
Very informative especially explaining what each post is and what function it performs. I have a 2001 GMC that I installed a 5.3 LS same year. As you know there's only one wire on that alternator for the ignition to signal when voltage is required to the battery. Because the old vortec set up used multiple wires. The brown wire is not used with the 5.3 so my battery lamp in dash sporadically illuminates but the voltage gauge reads 14ish volts when running. Can I tap the alternator batt light and connect in the dash to battery lamp or is the circuit tied into the PCM? THANKS
Hi, Bruno, i am very excited about this video, would you please send me notes on Bench test wire connections, mostly indicant light, battery terminals Pos and Neg to the alternator. My alternator has a two-point connector not three. Would you please help bro?
Question. I'm rebuild a car no electrical component in it yet just the engine. my alt not charging. It has the same Voltage as the battery. Is it because I don't have anything electrical running or the alt is done
ok so my old alternator will turn the light on but not off doing this test. i tried 2 new alternators 1 from a ford focus and a reman denso from a toyota and the light will light up if you touch the light ground to the case but not to any of the 3 pins on either of the new alts. so either i have 2 bad new alts or this test does not work for all common alternators.
Will upgrading the amperage in a cars alternator create more amperage coming out of the stock battery or must i replace the battery also to get more amps out of it???
S10 truck probably has a 95A alternator or somewhere around there. Does it cut out even when you rev then engine? A alternator will only produce peak current at around 3000 engine rpm. If it still dims when revving the engine, I'd bet your cables are undersized/ poor connection.
@@Mr05Tundra i never tried revving the motor so i dont know, im away from the truck now but the stereo system was professionally installed, the battery and alternator wires under the hood we're not upgraded though .. Are you saying the stock alternator is good enough? Upgrading it wont help?
@@babyjesus2025 I can't say for sure because I don't know what kind of power you're pushing. Cars are typically built to a minimum standard. Lights dimming is due to voltage drop, it can very well be your alternator but in most cases, it's undersized wiring from the alternator to the battery. If you install a bigger alternator, you must upgrade the wire sizing anyways so I'd start with the wiring. Some people install capacitors inline with the amp, that is a band aid fix to undersized equipment/wiring but it works.
@@Mr05Tundra thank you. Yes I'm going to upgrade the wires under the hood from Battery to alternator and grounds first but if that doesn't work can I just upgrade the alternator or do I have to upgrade the battery also???
@@babyjesus2025 you can leave the battery stock, when your car is running, all power comes from the alternator anyways, the battery for the most part is only getting charged when the car is running and not giving out any power.
I’ve got a B.B. Low Turn Alternator 1 wire red & White for the dummy light & my impact gun maxes out 2,000 rpm my issue is my battery in my gun ! Not getting the rpm
What do you mean by 'fry' the voltage regulator if it's not in series? LIke.. you make sure it's attached to the battery before it makes contact with the L connector? LIke.. that's the negative and the positive stud part can only be connected to 'under load' meaning, the battery needs to be in place? So cornfused..
The faster you turn the alternator, the higher the voltage will be. That's why you need the voltage regulator in order to make sure you don't send 28V to your cars electrical system when your reving your engine.
I was jumping a car and my battery died just from letting it charge there battery with there car off so my only guess is my alternator happened to be on its last leg at that point. I was able to drive home after getting a jump but barely had any power and the voltmeter on the dash was at 8 volts then jumped up to normal voltage then dropped back to 8 again so i guess mine was not charging consistently. Strange because the brushes are fine maybe the regulator went bad. Stinks because ebay has new ones for cheap and they are motorcraft but i need it asap so i have to pay over 200 at o reillys. When I spin the old one by hand I get 0.23 volts.
@@Mr05Tundra excellent, thanks heaps. Great video by the way, the only true bench test I could find on RUclips, all the rest are always inside the car.
Your talking about cutting the pulse width or field wire or whatever you called it it doesn’t matter on the 2011 and up GM’s? Actually it’d be 07’ to 13. Further more they have a 2 wire plug. So I’d warn anyone against choppin wires to get full output since he’s comparing apples to oranges. Additionally as if your weren’t wrong enough the BCM controls the 3-4 different charge rates
Tried using the same setup. the bulb didn't lit. I connected the positive on the B+ and the negative on the connector with (L) code. I'm checking my Denso alternator if its still working. Did I miss anything. Thanks
I checked the bulb by directly connecting it to the battery and it tested ok. Again i followed the connections in your video and it didn't light up. The positive of the battery is connected to the stud and battery negative is connected to the case of the alternator.
I'm willing to bet that your battery had a small short in it, keeping it from going any higher in voltage. Your other battery was fine with no problems in it, so it could go higher in voltage.
The exciter wire or "field" wire's voltage tells the alternator to begin charging the battery. When the ignition is in the run position without the engine running, 12.5 volts flows across the circuit, including through the "warning" lamp all the way to the "l" terminal on the alternator. The "l" terminal serves as a ground, making the lamp turn on. When the engine starts and is running, the alternator sends 12.5 volts back through the "l" terminal, thereby interrupting the ground, which in turn causes the light to go out. When this happens, the alternator also at the same time is turned on and starts sending voltage out to the battery through its"b" terminal. The lamp serves as resistance in the "exciter" circuit and is what ultimately tells the alternator to start charging. By bypassing the lamp, there is no resistance in the system or way to indicate a problem with the alternator.
@@Mr05Tundra If i take the wire directly from battery to bulb it works. When i connect it to the alternator positive and any of the pins for the plug it doesn't light up. Does the bulb have to be a big bulb? i used a side marker bulb and its a small bulb.
@@Mr05Tundra This is an alternator from an 02 ford focus. Three pins in plug and on the wiring diagram 2 wires go to PCM and 1 red wire goes to battery junction box to a fuse that says always hot and its a red wire on the plug.
Really i don't understand where to put all the wire connection. You must show step by step otherwise it will be easy to follow on how to check the alternator.
yes alt post to battery positive and alt case to ground. then the light to alt post and 1 of the pins on the connector. my old alt that wont charge will turn the light on but not off. the new alt i just bought wont even turn the light on. im pissed.
Great video. Glad I found it. Finally a great explanation on a 'hands on' description of the wires in the 3 wire connector and what each wire does. I will incorporate this in a bench test of an alternator I have suspected is bad sometime in the coming days. Appreciate you taking the time to make this and to post it.
Thank you very much for posting this video. You may not realize how important this information is. Thank you once again !
Great job - I really liked how it didn't quite work out the first time but you explained what the problem likely was and sure enough it worked great by the end. Thanks!
Why does this video not have more views?? This is awesome!
I just got a used one I can't spin it fast enough. I guess I'll just have to put it on the car and test there. Thanks for the video.
Didnt want to kill your 4:20 likes, making it 421, but it was the most informative video I've found within last hour, trying to find the answer for my case ))
Great video… I always pull this up when I need to try bench test an alternator at home.
The best explanation so far on who to test.
Glad it was helpful!
Thank you for this. I’ve learnt something today.
The bench test, just what I was looking for 💪. Subbed, belled
Thanks for the sub!
Great video. Explained very clearly. Thanks
Top video..well explained..Thanks bro
This is just the video I was looking for. When I test the voltage coming from the plug on the car, I get 5v. Is it possible that some alternator voltage regulators need 5v being supplied not 12v?
Very informative especially explaining what each post is and what function it performs. I have a 2001 GMC that I installed a 5.3 LS same year. As you know there's only one wire on that alternator for the ignition to signal when voltage is required to the battery. Because the old vortec set up used multiple wires. The brown wire is not used with the 5.3 so my battery lamp in dash sporadically illuminates but the voltage gauge reads 14ish volts when running. Can I tap the alternator batt light and connect in the dash to battery lamp or is the circuit tied into the PCM? THANKS
I believe they might use PWM on the newer trucks, hence the lack of wires used
Hi, Bruno, i am very excited about this video, would you please send me notes on Bench test wire connections, mostly indicant light, battery terminals Pos and Neg to the alternator. My alternator has a two-point connector not three. Would you please help bro?
In my experience some alternators need the I (ignition) wire to be connected to 12v before producing any charge
Really helpful video
Help us fix the Nissan Prairie Alternator 👍🏽
Buy a new one lmao 🤣
Really well done and well thought out. Thank you
thank god for you.. i solved a mystery :) thumbs up
Glad I could help!
Question. I'm rebuild a car no electrical component in it yet just the engine. my alt not charging. It has the same Voltage as the battery. Is it because I don't have anything electrical running or the alt is done
Thanks for sharing! Can an alternator go bad intermittently? I have a 03 that I suspect has a defective battery.
As it heat up possibly. More likely a voltage regulator to blame
Are you hooking the multimeter to the battery? How can it show 12.53v at the begining?
Yes, the alternator is connected to a battery
ok so my old alternator will turn the light on but not off doing this test. i tried 2 new alternators 1 from a ford focus and a reman denso from a toyota and the light will light up if you touch the light ground to the case but not to any of the 3 pins on either of the new alts. so either i have 2 bad new alts or this test does not work for all common alternators.
This was fantastic thank you so much! ...I have a gm 2 pin connector on mine...I assume L pin is still for the light?
Lamp/light
Thanks for this...very helpful to me...👍
Will upgrading the amperage in a cars alternator create more amperage coming out of the stock battery or must i replace the battery also to get more amps out of it???
S10 truck probably has a 95A alternator or somewhere around there. Does it cut out even when you rev then engine? A alternator will only produce peak current at around 3000 engine rpm. If it still dims when revving the engine, I'd bet your cables are undersized/ poor connection.
@@Mr05Tundra i never tried revving the motor so i dont know, im away from the truck now but the stereo system was professionally installed, the battery and alternator wires under the hood we're not upgraded though .. Are you saying the stock alternator is good enough? Upgrading it wont help?
@@babyjesus2025 I can't say for sure because I don't know what kind of power you're pushing. Cars are typically built to a minimum standard. Lights dimming is due to voltage drop, it can very well be your alternator but in most cases, it's undersized wiring from the alternator to the battery. If you install a bigger alternator, you must upgrade the wire sizing anyways so I'd start with the wiring. Some people install capacitors inline with the amp, that is a band aid fix to undersized equipment/wiring but it works.
@@Mr05Tundra thank you. Yes I'm going to upgrade the wires under the hood from Battery to alternator and grounds first but if that doesn't work can I just upgrade the alternator or do I have to upgrade the battery also???
@@babyjesus2025 you can leave the battery stock, when your car is running, all power comes from the alternator anyways, the battery for the most part is only getting charged when the car is running and not giving out any power.
This video is awesome
Thanks, glad you enjoyed it!
iS THIS A 2 WIRE ALTERNATOR WITH BUILT IN EXCITOR WITHIN?
No it's 4 wire
I’ve got a B.B. Low Turn Alternator 1 wire red & White for the dummy light & my impact gun maxes out 2,000 rpm my issue is my battery in my gun ! Not getting the rpm
What do you mean by 'fry' the voltage regulator if it's not in series? LIke.. you make sure it's attached to the battery before it makes contact with the L connector? LIke.. that's the negative and the positive stud part can only be connected to 'under load' meaning, the battery needs to be in place?
So cornfused..
Brilliant video, thank you for sharing.
Do you know the power of the drill?? 1/3HP or 1/4 ETC???
Hello
Just I want relationship between alternator speed and voltage can you please post this...
The faster you turn the alternator, the higher the voltage will be. That's why you need the voltage regulator in order to make sure you don't send 28V to your cars electrical system when your reving your engine.
What can you use instead of a bulb?
I was jumping a car and my battery died just from letting it charge there battery with there car off so my only guess is my alternator happened to be on its last leg at that point. I was able to drive home after getting a jump but barely had any power and the voltmeter on the dash was at 8 volts then jumped up to normal voltage then dropped back to 8 again so i guess mine was not charging consistently. Strange because the brushes are fine maybe the regulator went bad. Stinks because ebay has new ones for cheap and they are motorcraft but i need it asap so i have to pay over 200 at o reillys. When I spin the old one by hand I get 0.23 volts.
Does it matter what directing you spin it?
Good question! Shouldn't matter because it's 3 phase Ac rectified to Dc
@@Mr05Tundra excellent, thanks heaps. Great video by the way, the only true bench test I could find on RUclips, all the rest are always inside the car.
Excellent!! Thanks
Glad you liked it!
Your talking about cutting the pulse width or field wire or whatever you called it it doesn’t matter on the 2011 and up GM’s? Actually it’d be 07’ to 13. Further more they have a 2 wire plug. So I’d warn anyone against choppin wires to get full output since he’s comparing apples to oranges. Additionally as if your weren’t wrong enough the BCM controls the 3-4 different charge rates
How you did connection can you please show it to us
Tried using the same setup. the bulb didn't lit. I connected the positive on the B+ and the negative on the connector with (L) code. I'm checking my Denso alternator if its still working. Did I miss anything.
Thanks
Does the bulb light up?
No. The bulb didn't lit, but i tried to connect the bulb directly to the battery and its tested ok.
@@bengiw1 and your testing this while having the battery connected to the alternator (stud on the back positive and negative on alternator case)
I checked the bulb by directly connecting it to the battery and it tested ok. Again i followed the connections in your video and it didn't light up. The positive of the battery is connected to the stud and battery negative is connected to the case of the alternator.
@@bengiw1 well it should light up so I'd say your regulator is no good
Hi , thank you man , perfect , 👌👍🙏
You're welcome!
I'm willing to bet that your battery had a small short in it, keeping it from going any higher in voltage. Your other battery was fine with no problems in it, so it could go higher in voltage.
Good video OP
Once I have everything connected the bulb doesn't light up, I know the bulb works and the battery is charged, any ideas?
Could be a bad regulator
The brown wire is to charge/ turn on the regulator for alternator to put out power.
Is it normal for my 12 v alternator to read 25 v out of the alternator ?
No, it's most likely a defective regulator
Thanks for the help
You need to hook up an amp meter to show the amount of amps it is producing......volts is not the only test to see if the alternator is good......
Why can't you just connect a voltmeter to the + terminal and ground on the alternator when it is spun? Why the light bulb?
The exciter wire or "field" wire's voltage tells the alternator to begin charging the battery. When the ignition is in the run position without the engine running, 12.5 volts flows across the circuit, including through the "warning" lamp all the way to the "l" terminal on the alternator. The "l" terminal serves as a ground, making the lamp turn on.
When the engine starts and is running, the alternator sends 12.5 volts back through the "l" terminal, thereby interrupting the ground, which in turn causes the light to go out. When this happens, the alternator also at the same time is turned on and starts sending voltage out to the battery through its"b" terminal. The lamp serves as resistance in the "exciter" circuit and is what ultimately tells the alternator to start charging.
By bypassing the lamp, there is no resistance in the system or way to indicate a problem with the alternator.
Where the multimeter leads connecting to
So if the light doesn’t come on when connecting the bulb to any of the pins on alternator does that mean it is bad?
Can also be because the bulb is burnt or bad wiring, if the bulb is burnt, the alternator will not charge
@@Mr05Tundra If i take the wire directly from battery to bulb it works. When i connect it to the alternator positive and any of the pins for the plug it doesn't light up. Does the bulb have to be a big bulb? i used a side marker bulb and its a small bulb.
@@Mr05Tundra This is an alternator from an 02 ford focus. Three pins in plug and on the wiring diagram 2 wires go to PCM and 1 red wire goes to battery junction box to a fuse that says always hot and its a red wire on the plug.
@@robcat7499 you can use a side marker bulb, that's no problem. It's most likely the voltage regulator acting up, that would be my guess
Thank you very much!
For parts to repair alternatorstarterrebuildkits.com/product/ad244/
Great
Really i don't understand where to put all the wire connection. You must show step by step otherwise it will be easy to follow on how to check the alternator.
kind of skip to step their didn't you? I believe you have to hook a battery up to the alternator first otherwise everything you're doing is useless.
yes alt post to battery positive and alt case to ground. then the light to alt post and 1 of the pins on the connector. my old alt that wont charge will turn the light on but not off. the new alt i just bought wont even turn the light on. im pissed.
Good morning
I’m to stupid for this, I couldn’t understand one bit :/