For some strange reason - the battery light in my wife's volvo 850 (1995) is staying on when the car is OFF. It got so bad that my Father-in-law paid for a AAA battery because the car was not starting.. which I thought was a boneheaded move because the battery that was in there was less that 2 years old. (I was not on the scene when this happened)

I recently took the car to Autozone, and they did say that the Alternator was only putting out 13.6V rather than the standard 14v that the alt was supposed to do. This was before teh battery was exchanged...

But what is flumoxing me is the fact thatthe light is ON when the car is OFF. When the car is running - it's not on... Is it the alternator?

So what the hell is this about? PLEASE HELP!!

 

The amount of voltage an alternator puts out is second to the amperage. If called to do so the alternator in an 850 should put out close to 100 amps, it's what they are rated at. The voltage will vary depending on the state of charge of the battery and the amount of accessories operating at the time of the test. 13.6 volts is NOT below normal, having a charge or battery light on is.

The alternator may be bad but if it were it's because one or more of the diodes had gone bad and is allowing the battery to discharge through the alternator. It's fairly rare but it's difficult to catch. The alternator will charge properly when it's running (like your light being out) but when you shut it off the battery starts to feed current back through the alternator so it acts like a big light bulb draining the battery but nothing physical to warn you it's happening (except maybe that charge light). You need to check for a draw and find out what is causing it.

If you pull the big wire going to the alternator and the light goes out you likely have a bad alternator. If you take it in and have it bench tested it will likely pass even if it has this fault as most testers are looking at what the alternator can produce rather than if there is a "leak" !!

Any chance you can get the old (2YR) battery back ?? Should have been under warranty.

 

There was a wire loose on the alternator.. will post a pic here in a bit - its the red and white one below the main charging wire...this isn't the first time i have ssen this happen..I pushed it back in and the battery light immediately went out...

 

Here's the wire I was talking about....



What is this wire any way?

 

It's the alt voltage output sense for the idiot light; with key on but alt output voltage is below battery voltage (like when it's not turning or has a fault) then the light is on. When alt output is equal or greater than battery voltage then the light goes out.

 

so do think this had anything to do with the light staying on AFTER the car was off, and therefore causing some sort of drain? I am assuming so because it is off now....