Mechanics

WHY IS MY CHARGING LIGHT STILL ON?

1994 Subaru Wagon • 265,000 miles

I just replaced the alternator myself in the shop parking lot after they told me it was bad. I had been having charging issues. I drove it home fine and the charge light was not on. That was two days ago. I just went to drive it, and the light remains on. I have a good charge, and the alternator is installed properly, but the light remains and I'm afraid I'm draining the battery again. Best I can tell, the voltage output is good. All connections and belts are tight. I'm about at my wits end with this car. Six months ago I was having a similar issue and it turned out a couple wires in the harness just over the alternator were melted. The shop fixed that and I didn't have problems until two weeks ago. And yes, I trust this shop.
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Jdflight
December 15, 2011.



So at idle with the charge light on what is the viltage reading at the battery cables at the battery?

Saturntech9
Dec 15, 2011.
12.8 ish. I don't remember exactly since I tested it a couple hours ago, but it was definitely good.

Here's a fun twist. I went back out to test the voltage at the battery and the alternator and took my wife to run the accelerator. Everything was testing fine, and I had her run it up to 3500 to test at elevated rpm. The light went out. It hasn't come on since. I took it to O'Reilly for a separate errand and had them check it. They said it tests fine, but the battery is a bit low (makes sense since it was completely drained from the bad alternator.

So, two questions. Would a low battery cause the light? I thought it only came on with a charging issue. If so, why would it have been extinguished as soon as the new alternator was in the entire way home, then come on when I started it again?

Tiny
Jdflight
Dec 15, 2011.
Are you sure you dont have a bad battery?A bad battery can skew the charging voltage. Also have you checked the battery cables to make sure there clean and tight?Have you checked the negative battery cable to ground using a ohms meter yet?

Saturntech9
Dec 15, 2011.
The battery test O'Reilly did yesterday said it was good, just a bit low. I'll deep charge it next week when I have access to a charger. I haven't personally checked the neg to ground. The cables are relatively clean and yes, tight.

Tiny
Jdflight
Dec 16, 2011.
I would check the negative battery to ground and also the case of the alternator to ground.

Saturntech9
Dec 16, 2011.