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Mysterious Battery Light PLEASE HELP

05-06-2022, 08:11 AM
A few days ago my son left a dome light on in our Civic. (05 Ex Special Edition 1.7L).
Dead battery. Jumped the car, drove it for chores for 2 hours. Got home. Went to start it again. Dead.
Took to have charging system checked, said alternator was putting out under 12V when under load. Recommended changing.

So! I bought a Reman Advance Auto Alternator and put it in. I also put in a brand new battery. Checking the charging system it's around 13.5-14 at Idle and doesn't drop under load. Problem solved right?...Wrong!

When the car warms up to operating temperature. While driving. If you apply the brakes and come to a stop. The battery light will flicker on and go back off. Sometimes it's a quick blink. Sometimes it's a few seconds. But it's every time. And only when the car is warmed up. Won't do it first thing in the morning.

I immediately thought I got a faulty Alternator. But every time Advance checks it, or I do with a multimeter. It's putting out great. And they said they won't swap it unless it fails a bench test. Which I doubt it will.

So I tried other avenues. Here is what has been done:
Brand new Positive Battery terminal
Brand new Negative Battery Cable/Terminal
Checked 80a battery fuse and 20a alternator fuse
Replaced Electronic Load Detector
Checked for continuity between battery and Alternator.
Replaced starter (While I was in there anyway)
Tore back down and ensure all bolts/tensioners/belts were tight

I even had her put it in park and I started to "jostle" components/wiring to see if something was loose and causing it to lose connection and I wiggled everything I could wiggle. No battery light.

It ONLY happens when coming to a stop when the car is warmed up.

Guy at Advance said maybe a fault in the brake switch or a short to the brake lights. But you can APPLY the brakes all you want and it won't come on. Only when coming to a stop. Like something is shifting. But I can't find it.

Should I ignore this? The light goes right back off, so I am assuming whatever is happening is breif. Every time we check the Alternator is putting out close to 14V. Should I tear it out again and have it bench tested? Is this a short to that battery bulb? Or does it require more voltage when actually stopping with the brakes and is dropping below thresh hold and it's a brake issue? What am I missing? It's driving me nuts...and Broke.

Sorry for the long post. But any help would be appreciated.

05-06-2022, 11:18 PM
Hate electrical problems...

Sounds like a loose ground maybe. If not--

Perhaps a full reset would help? Disconnect both battery terminals (car off of course) and hold them together for maybe 15 seconds. This should completely drain everything and reset the computers.

Let us know....

Edit: one more thought. Since only when coming to a stop maybe there is a slight sideways pressure applied to the brake pedal when moving from gas? Yeah a crazy ides but the okder brake switch could be sensitive to it. 🤷*♂️

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