I searched but couldn't find an answer to my problem.
The issue i am having is that 2 days ago at night, my battery and brake lights turned on, and this usually means a bad alternator, but my car seems to drive fine with no dimming of lights or any of the sort, starts up fine and all. I disconnected the positive battery terminal with the car running to test if the alt was feeding off the battery but it wasn't. Earlier this same day before the test, i took it to a mechanic and the device he plugged into my battery terminals was reading 12'ish volts.
I'm clueless as to what's going on. Is my alternator about to go regardless even though my car didn't turn off when i disconnected the terminal ?

Thanks for the link, i read it but my lights are still on. I even changed my alternator fuse and the lights still show up. I also tried the disconnecting the negative terminal and the car kept running.
I'm clueless... Maybe the alternator is behaving good for now but its on its last days. I don't know what to think of anymore.

Check the alternator charge back wires for being loose, or corroded. I bet if you had the terminal off for long enough it will die...No recharge from alt..Then try turning on all of your acessories and see if the car dies, with the terminals connected..Do you yourself have a volt meter of some kind, or does your guy do most of it? Like when you had your radio installed!!

I took it my mechanic and he connected the voltmeter to my battery and it was reading i believe was 12.8-9 volts. Obviously this isn't good but still no sign of my lights dimming down or starting problems of that sort.

12.6 is normal..It's not too far over..Was this at idle?

Also your gauges is not in your profile...But I'm guessing you don't have a volt gauge..

No volt gauge, and when he did the test it was at idle.

Drive her at night...If your lights are brighter than normal, then I would start to worry..But sounds like you should be fine...

What is your idle set too anyway,Above stock?

But yeah check your chargeback wires from alt to batt, just to make sure...

I took her for a long spin friday night and lights were normal. I'll check up on the wires, and idle is at 800rpm. Thanks bud.

AH i just started having this problem last night, and my lights ARE brighter than normal. increasing with engine load in fact. at idle the brake and battery lights will go off and everything will dim. im figuring alternator gone?

Scooped-Yeah if your lights are brighter than normal, its going to go out soon..I wish I could tell you otherwise but, unfortunetly that's not the truth..Unless you want me to lie to you which, would not really help you at all..If you have aftermarket stereo, you might want to look into the canadian alternator, it charges more.As opposed to the oem (usa) alt..

a good alt and charging system should give you 14.67Volts on a multimeter at idle at your batt posts with no load, typically with corrosion and old cables etc you will get 14.2-14.3ish volts anything below 14 and you have a problem. then retest by putting your vehicle under load: turn on all lights, a/c, windshield wipers, blower motor etc to put load on the engine you still should not be below 14 volts. if your getting 12v at idle at your batt posts check the voltage right off your alt: toutch the red lead of your multimeter to the bolt connected to the red wire on the back of your alt (caution do not arc it to power and ground otherwise you will start arc welding) then toutch the black wire of your multimeter to the case of the alt and now if your getting 14v then you have bad grounds/wires and need to do further voltage drop tests to diagnose which wire/ ground it is.
hope this helps

Wow. I am so glad someone else stepped into this before me.

12 is bad, just to let you know. 14+ is good.

Also never disconnect your positive battery terminal and see if your car keeps running. If you have an older car with carburetors (say like a 69 camaro) this will work. On newer cars that have ECU's in them (like your car) you are taking the chance of frying the ECU, frying pigtails together, blowing relays, and blowing fuses. New cars have to many features for you just to go and break the closed loop of the charging system. So wish you luck.

I would pull the alternator off of your car, take it to your parts house and bench test it. This will give you a very accurate reading of what your alternator is doing.

Also if you have no knowledge of stuff, do not post bad ideas that will cost more in the long run.

Thanks for the info guys. Looks like the alternator shitting teh bed then. On it's last days, hopefully i don't get stranded.

Ya what the hell was I thinking..these guys are right, it should be charging at around 14 volts..I'm really just thinking it's the chargeback wires that are corroded or something, making it read 12 volts at idle..Did he hook up the amp clamp? That's an easy way to notice if it's overcharging, or not charging enough..

You already drove her at night and didnt't notice anything unusual..Also your not popping fuses, which is good and bad at the same time...If no fuses pop, it make a little harder to diagnose where the problem with the wiring is..

Ok i ran into another pproblem with my dsm. -.-" one after another huh.. so this time the brake and the battery llights keep goin on and off. It been like for about two weeks now. I kinda think its the alternator since i got a rebuilt one from autozone lik 3 weeks ago. The battery and brake light only goes on after the car is heated up. I took out the volt meter and checked the battery. with the engine off, the battery was at 12.5xx volt and with the car on its at 14.5xx. Is the alternator overcharging? i actually went through two alternator. The first one died like couple hours after the battery and brake light came on. The next one died without having those lights coming on. So any ideas? I do have a lifetime on it. But I'm too lazy to take it off and bring it there to have em check out.Thanks guys

i just had the same prob with my wifes 97 spider its the alternator.

You can definitely rule it IS the alternator by checking the voltage when the lights come on, while engine is running. If it's pushing out 15.5+ volts you can bet it's the alternator, however, if the lights are coming on because of a voltage drop it could be something else such as a ground or wiring issue. I always keep my radar detector on voltage reading, it's nice to know right away if your over-charging or if a cop is pointing radar.

Edit: 14-14.5 volts is perfectly fine when running. I run 14v and my alternator has 0 miles and about 60 seconds on it. (Just replaced it).

Yea both the lights goes on at the same time. How many grounds are there for the 2g alternator? it comes on and off.. really annoying.. keep thinking its gonna die on me.

Having the three dash lights on (battery, coolant, and brake) does NOT necessarily mean that your alternator is dead. It means that there IS a problem with your charing system. Yes it could be your alternator but it could just as easily be your ALT fuse, the big 80 amp fuse in the corner of your fuse box. It is much easier (and cheaper) to check the fuse than to pull our alternator out so I recommend checking the fuse first.

This happened to me today and it was fixed within a few minutes! Gotta love dsmtuners! Awesome site!

Don't forget 80amp alt fuse is held in with a screw on the side and smarter to remove screw 1st than pull a magilla gorilla and try and rip it out

91Bomb said:

Don't forget 80amp alt fuse is held in with a screw on the side and smarter to remove screw 1st than pull a magilla gorilla and try and rip it out

Click to expand...

It is actually held in with two 10 mm bolts. And yes you are right, just tugging on it won't do any good. Take off the two bolts and it will slip right out.

So, I've had two alternators go on me before. One was putting out low voltage, dash lights dimming, battery/brake light on, car dying, etc. Second overvolted, again the battery/brake lights coming on, along with my stereo amps cutting out, fan/lights getting brighter/faster, etc.

Most recently, my car was out of business for a few months, just got it back up running, but battery was just about dead. I put in an old battery, but was again noticing overvolting symptoms, but figured this 2nd battery wasn't holding voltage well and the alt was overcompensating or something. Bought a brand new battery and same thing. However, this time, it has been intermittent, only overvolting on some drives, but there have also been times it doesn't seem to be charging at all (seen battery voltages from 10.2 to >17).

One strange thing: the battery/brake lights never come on.

The brake light comes on with the parking brake. I thought maybe the battery light was blown and being a critical part of the charging system, thought it might be the issue, but I swapped the bulb with another that did light up and no change. Also, I thought those lights were supposed to light up when you turn to ACC/On, but they don't come on then either.

I'm awaiting another alternator for this week, but I'm concerned I have something electrical going on rather than the alt.

I've tried:
1. checking the alt connector, is in fully, wires intact.
2. Charging cable is 4ga, just installed earlier this year, in parallel with the stock wiring.
3. Main battery/chassis ground was replaced and is still intact.
4. Alt fuse was replaced earlier this year and looks intact (new wiring still thru the fuse)
5. A different ECU, no change.
6. Removed the alt "relay", no change.
7. as above, checked dash battery light, bulb intact and tested in another socket
8. Checked for blown fuses elsewhere, only found one in the interior box, replaced with no change.

Has anyone seen this happen? Any other ideas for the cause? I've had both sides of a bad volt reg in my alts, but the dash lights always came on. Not sure why this is not happening now.

If the alts were not oem mitsubishi that could explain things since aftermarket alts are known to do this on our cars. Once I put 3 pep-boys alts in my car in 2 mths time and still had problems until I went and got a mitsu alt.

First two were not mitsu (first was unknown, second was an alterstart high output). My current one is mitsu, picked up from a junker, but worked great up until I got my car up and running again.

Currently, doesn't seem to be charging well as idle voltage is around 12.4V at the battery.