# How to test alternator... **URL:** \ **Category:** SON240sx Automotive\ **Created:** [July 5, 2006, 5:11pm UTC](https://forums.speedlife.net/t/how-to-test-alternator/97674 "2006-07-05T17:11:16Z")\ **Posts on this page:** 16\ **Page:** 1
**Author:** ![DWillms2](https://avatars.discourse-cdn.com/v4/letter/d/cab0a1/32.png) [@DWillms2](https://forums.speedlife.net/u/DWillms2)\ **Post date:** [July 5, 2006, 5:11pm UTC](https://forums.speedlife.net/t/how-to-test-alternator/97674/1 "2006-07-05T17:11:16Z")
Hey all, Car’s almost all put together, but I think I have an alternator problem. The battery light and the parking brake light both stay on no matter what. I looked up the parking brake light staying on, and supposedly it can be triggered by the brake fluid level switch, and the brake fluid level switch can be triggered by low batt/ alternator, correct? [http://www.sr20forum.com/showthread.php?t=92460](http://www.sr20forum.com/showthread.php?t=92460) Anyways, I replaced the battery, so that’s all good, is there any way to test the alternator easily, without digging through the entire front of the engine… It’s on a 95’ 240 with a ka24de btw. Thanks! ---
**Author:** ![flyingchicken](https://avatars.discourse-cdn.com/v4/letter/f/ac91a4/32.png) [@flyingchicken](https://forums.speedlife.net/u/flyingchicken)\ **Post date:** [July 5, 2006, 7:46pm UTC](https://forums.speedlife.net/t/how-to-test-alternator/97674/2 "2006-07-05T19:46:06Z")
go to midas and they’ll do a battery diagnostic for 20 bucks ---
**Author:** ![Eggman](https://avatars.discourse-cdn.com/v4/letter/e/e99b99/32.png) [@Eggman](https://forums.speedlife.net/u/Eggman)\ **Post date:** [July 5, 2006, 8:16pm UTC](https://forums.speedlife.net/t/how-to-test-alternator/97674/3 "2006-07-05T20:16:19Z")
Just use a multimeter over the terminals of the battery and see if it reads 14.2V or anything close. Some Midas are willing to do the test for free. ---
**Author:** ![DWillms2](https://avatars.discourse-cdn.com/v4/letter/d/cab0a1/32.png) [@DWillms2](https://forums.speedlife.net/u/DWillms2)\ **Post date:** [July 5, 2006, 9:20pm UTC](https://forums.speedlife.net/t/how-to-test-alternator/97674/4 "2006-07-05T21:20:55Z")
Ya, I did that, and pulled off the neg terminal when it was running, either my alt is shot or I have a bad connection, cause it was reading 12.2 volts running or not, and also died with the neg connection taken off… ---
**Author:** ![scribbles](https://avatars.discourse-cdn.com/v4/letter/s/bb73d2/32.png) [@scribbles](https://forums.speedlife.net/u/scribbles)\ **Post date:** [July 5, 2006, 9:39pm UTC](https://forums.speedlife.net/t/how-to-test-alternator/97674/5 "2006-07-05T21:39:04Z")
I have an alternator tester at MSSC bring it over and I’ll do it for free and tell you if it’s good or not. ---
**Author:** ![Eggman](https://avatars.discourse-cdn.com/v4/letter/e/e99b99/32.png) [@Eggman](https://forums.speedlife.net/u/Eggman)\ **Post date:** [July 5, 2006, 11:13pm UTC](https://forums.speedlife.net/t/how-to-test-alternator/97674/6 "2006-07-05T23:13:07Z")
> [@DWillms2](#): > > Ya, I did that, and pulled off the neg terminal when it was running, either my alt is shot or I have a bad connection, cause it was reading 12.2 volts running or not, and also died with the neg connection taken off… I don’t quite understand what you mean. Why did you pulled off the neg terminal? Of course the car will die if you pulled off the terminal. That has nothing to do with the alternator. ---
**Author:** ![DWillms2](https://avatars.discourse-cdn.com/v4/letter/d/cab0a1/32.png) [@DWillms2](https://forums.speedlife.net/u/DWillms2)\ **Post date:** [July 6, 2006, 10:57am UTC](https://forums.speedlife.net/t/how-to-test-alternator/97674/7 "2006-07-06T10:57:18Z")
:lol: Dunno, saw it on some other site… Guess they were wrong… Anyways, it wasn’t charging at all, volt’s went down like 0.5v when running, didn’t matter if you revved it or not… And scribbles, I would take you up on that offer, but it may be quite a far drive from Saskatchewan to test an alternator :lol: ---
**Author:** ![Eggman](https://avatars.discourse-cdn.com/v4/letter/e/e99b99/32.png) [@Eggman](https://forums.speedlife.net/u/Eggman)\ **Post date:** [July 6, 2006, 3:57pm UTC](https://forums.speedlife.net/t/how-to-test-alternator/97674/8 "2006-07-06T15:57:48Z")
hey man, you said its 0.5V lower when its running. Does that mean its running at 13.7V? That’s a little weak but still won’t die on you. The voltage is not suppose to jump up even if you rev it… Suppose to stay at around 14.2V. Its kind of hard to explain to you how it works. ---
**Author:** ![luka](https://avatars.discourse-cdn.com/v4/letter/l/a587f6/32.png) [@luka](https://forums.speedlife.net/u/luka)\ **Post date:** [July 6, 2006, 4:25pm UTC](https://forums.speedlife.net/t/how-to-test-alternator/97674/9 "2006-07-06T16:25:39Z")
goto any auto motive store… crappy tire… parts source… etc. actually. goto atleast two, 'cause I had an alternator tested at crappy tire and they said it was garbage… but then I went to part source they told me it was good… btw… the test are free. you have nothing to lose. ---
**Author:** ![smurf6x6](https://avatars.discourse-cdn.com/v4/letter/s/bcef8e/32.png) [@smurf6x6](https://forums.speedlife.net/u/smurf6x6)\ **Post date:** [July 6, 2006, 7:06pm UTC](https://forums.speedlife.net/t/how-to-test-alternator/97674/10 "2006-07-06T19:06:07Z")
You can volt test the battery but that still does not tell you if your alternator is compeletely good. Take it some place so they can run a avr test. They will amprage test the alternator when they do this. ---
**Author:** ![DWillms2](https://avatars.discourse-cdn.com/v4/letter/d/cab0a1/32.png) [@DWillms2](https://forums.speedlife.net/u/DWillms2)\ **Post date:** [July 6, 2006, 8:07pm UTC](https://forums.speedlife.net/t/how-to-test-alternator/97674/11 "2006-07-06T20:07:59Z")
No voltage is only like 12.5 Volts when sitting, 12.2 when running. And if I go an take it out for a drive, when I come back it’s like .1 or .2 lower, so obviously the alternator is not working, or is not wired properly. I’m gonna head to a salvage yard and find an alternator tomorrow? What vehicles is the alternator the same. All ka24de’s? Are s13’s the same as s14’s? Thanks! ---
**Author:** ![BlitzSix](https://avatars.discourse-cdn.com/v4/letter/b/dec6dc/32.png) [@BlitzSix](https://forums.speedlife.net/u/BlitzSix)\ **Post date:** [July 6, 2006, 11:02pm UTC](https://forums.speedlife.net/t/how-to-test-alternator/97674/12 "2006-07-06T23:02:06Z")
> [@Eggman](#): > > [quote=DWillms2]Ya, I did that, and pulled off the neg terminal when it was running, either my alt is shot or I have a bad connection, cause it was reading 12.2 volts running or not, and also died with the neg connection taken off… I don’t quite understand what you mean. Why did you pulled off the neg terminal? Of course the car will die if you pulled off the terminal. That has nothing to do with the alternator.[/quote] AFAIK a car shouldn’t die if you pull the neg terminal off, it should just run stragiht off the alternator without the battery. You obviosuly won’t be able to start it if you turn it off, but it should stay running ---
**Author:** ![Eggman](https://avatars.discourse-cdn.com/v4/letter/e/e99b99/32.png) [@Eggman](https://forums.speedlife.net/u/Eggman)\ **Post date:** [July 6, 2006, 11:37pm UTC](https://forums.speedlife.net/t/how-to-test-alternator/97674/13 "2006-07-06T23:37:20Z")
> [@BlitzSix](#): > > [quote=Eggman][quote=DWillms2]Ya, I did that, and pulled off the neg terminal when it was running, either my alt is shot or I have a bad connection, cause it was reading 12.2 volts running or not, and also died with the neg connection taken off… I don’t quite understand what you mean. Why did you pulled off the neg terminal? Of course the car will die if you pulled off the terminal. That has nothing to do with the alternator.[/quote] AFAIK a car shouldn’t die if you pull the neg terminal off, it should just run stragiht off the alternator without the battery. You obviosuly won’t be able to start it if you turn it off, but it should stay running[/quote] I’m not 100% sure on this, but may be 90% sure. The alternator is only connected to the battery. It charges the battery while its running. If you take out the terminal, then you have an open circuit. The car die. ---
**Author:** ![BlitzSix](https://avatars.discourse-cdn.com/v4/letter/b/dec6dc/32.png) [@BlitzSix](https://forums.speedlife.net/u/BlitzSix)\ **Post date:** [July 6, 2006, 11:47pm UTC](https://forums.speedlife.net/t/how-to-test-alternator/97674/14 "2006-07-06T23:47:25Z")
I dunno let’s wait for someone smart to chime in ---
**Author:** ![flyingchicken](https://avatars.discourse-cdn.com/v4/letter/f/ac91a4/32.png) [@flyingchicken](https://forums.speedlife.net/u/flyingchicken)\ **Post date:** [July 7, 2006, 6:22am UTC](https://forums.speedlife.net/t/how-to-test-alternator/97674/15 "2006-07-07T06:22:50Z")
you can have a partially dried out battery (as in, no more power) and charge it by starting the car…let it idle for 2 min, and take off the neg ternminal, if the engine still runs, your alternator is charging and working fine. you can also determine if your car is charging or just running on pure battery. as you take the neg off, the engine gets quiet. but once u put the neg back on, it gets louder (normal volume). that means your alternator is working fine. if your engine dies after taking off the neg, your alternator is gone thats what i tired after changing alternators also…ka24e alternator = ka24de alternator ---
**Author:** ![DWillms2](https://avatars.discourse-cdn.com/v4/letter/d/cab0a1/32.png) [@DWillms2](https://forums.speedlife.net/u/DWillms2)\ **Post date:** [July 7, 2006, 10:07am UTC](https://forums.speedlife.net/t/how-to-test-alternator/97674/16 "2006-07-07T10:07:04Z")
> [@flyingchicken](#): > > also…ka24e alternator = ka24de alternator Nice, should be much easier to find. Thanks!