Battery and Brake lights staying on.

[gprix1]

I had a battery and alternator go bad on me last week so I replaced both and now the alternator is charging fine and battery is at full voltage. In fact, the car is working great but when the old alternator died, both the battery and brake lights lit up on my dash as I limped it home. Now, even with both replaced and the charging system working good again, the battery and brake lights are still both dimly lit (looks much brighter in the picture below than it really is).

I've searched various forums and found some posts where others have had this issue but there was never any resolution to the problem. I checked all the connections, ground wires, ALT fuse, etc. and everything looks good. I have Link v3 configured to represent battery voltage on the factory boost gauge and as you can see in the pic below, it is good. That position is around 14.2v in my logs and stays there both idling and while driving.
I'm hoping this time someone might have an answer.

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[gprix1]

This is pretty much exactly how the other threads on this subject ended. I can't believe this hasn't been figured out before. Oh well, it's not affecting anything at the moment so I'll just deal with it for now. I have other things to work on with my car right now.

 

[liquidsilver]

Tried swapping the ECU? Are you using an OEM alternator?

 

[Moonlight GSX]

Have you checked the gauge cluster itself?

 

[Zex4g63]

A blown fuse under the hood will make it do that.

 

[gprix1]

I've been researching how alternators work and now I think I know what is wrong. Even though the alternator is brand new (well, rebuilt really), most likely a diode is bad on the alternator. Here is a very informative article on how an alternator works.
Pelican Technical Article: Alternator System Troubleshooting

The bottom line is that in order for your light to light, you must have a net imbalance in the outputs of the D+ and B+ sections of the alternator (or between the D+ output and the battery voltage, which amounts to the same thing).

Apparently, a failed diode can allow a back-feed of electricity which powers on the dash light dimly. I'll be pulling it soon to get tested.

 

[gprix1]

Yup, sure enough, replaced the alternator and it fixed it perfect. Logging 14.1v and 13.8v with all accessories. Now we just bought a '95 AWD Talon for my girlfriend that is doing the same thing so I guess it's time to buy (sigh..) another alternator. At least now I know for sure how to fix it.

 

[crazyquik22023]

Like Zex4g63 said, check your fuses under the hood. If one of those is blown and you might not notice it, such as the headlamps fuse, both the brake and battery light will be on on the dash.

 

[gprix1]

Checked the fuses, it was the alternator. It's fixed now.

 

[mattasi]

Yep, the brake and battery light on, almost always is a sign of a bad alternator.

 

[Archer Fabrications]

I just replaced my alternator with an oem one and these lights are flickering (like a loose grounding commection) my e break light switch is un plugged so i fogured it would short on something and light, however not the battery light. I'm hoping it's mot the brand new oem alternator, I'll be checking fuses and where the harness is disconnected from the e break.

This is the first time i drove the car since july 1st. And an alternator is the only new thing.

The pig tail wires are a bit fried though.

 

[wishihadatalon]

I just replaced my alternator with an oem one and these lights are flickering (like a loose grounding commection) my e break light switch is un plugged so i fogured it would short on something and light, however not the battery light. I'm hoping it's mot the brand new oem alternator, I'll be checking fuses and where the harness is disconnected from the e break.

This is the first time i drove the car since july 1st. And an alternator is the only new thing.

The pig tail wires are a bit fried though.

I had this exact issue after replacing an alternator with a rebuilt one. While I got the correct voltage and everything was fine, I still had the lights. After convincing the place that I purchased the alternator from that it was indeed the alt, I put in another rebuilt one and the issue went away.

 

[Archer Fabrications]

I got the oem alternator from STM, brian if your reading maybe you can help me out.

 

[1990dsmkid]

Do your interior lights, radio, windows, headlights and all that stuff still work? If so its not the alt fuse.