I had a flat battery, now replaced alternator is nearly new. Cannot get rid of alternator/battery warning light!!!

 

Probably an incompatible alt. Best bet is to use one that is suitable.

 

Thanks.
Alternator was replaced in Feb no lights until flat battery. Got the right battery fitted light still on. Can it be reset?

 

Is the battery being chrged and in good condition?

 

Please define "flat" battery. Was it merely discharged, meaning either it was not getting a proper charge or something was draining it when not running? Those conditions are not the battery's fault.

Or did the battery itself fail, meaning it would not hold a charge or it had failed a load test? If the battery has failed, exactly how was this determined?

Big differences for troubleshooting, so some more details would help.

 

I agree with JagV8. Only install a Jag alt. Aftermarket will keep the bat light lit.

 

I have a problem with battery light flashing on/off when ignition is turned on (before starting) The alternator is charging ok.

 

I think I'd go hunting for an electrical drop / loose/bad connection or the like.

 

I looked in the owner's manual and couldn't find anything about the battery light flashing before start. It only mentioned the light coming on steady for a charging system fault while driving. Does the light extinguish as normal after you start the engine?

Also, what year is your car? Any recent electrical system work?

 

Hi Carl. The battery light is out when engine is running. Alternator voltage output 14.6v. The check engine light is next to battery light. They both flash on and off briefly even before start up. engine light out while engine running. Had power window issues. This all started after battery was replaced. 2002.5 S TYPE 4.0V8

 

I'm officially baffled. I don't know of any scenario where either light flashes before engine start. Both lights should come on steadily as a bulb check before start, and then extinguish once the engine starts.

The check engine light can flash with the engine running if potential catalyst damage is sensed, but that almost always requires running for several minutes. It's not something you'd typically see with the engine cold.

Is this flashing steady, as if commanded on/off by a control module? For an example, think of a turn signal. Or is it more of a random flickering, with no consistent pattern, such as from a loose connection? And do the two lights act up in sync or independently?

Edit: You mentioned a new battery. Please hook it up overnight to an automatic charger with at least a ten amp output. New batteries often aren't fully charged at time of purchase. Low prestart voltage can cause some funky behavior that makes no sense, even if the engine seems to start normally. Try charging the battery for giggles and see if the symptoms change.

 

No. Both lights come on for a milli second and then go out. They don't come on again. The only light iluminated is the oil, and that goes out when car starts.

 

the light can be cleared once you fix the issue turning it on. you have a fault in the system still or again. a battery with a bad cell can do this, but you need to check voltages running at the back of the alt B+ and the battery. they should never be more than a >2voltage drop or there's a poor connection from resistance, loose, corroded etc

 

I checked the voltage at the alternator and am getting a 0.3 volt loss at the battery. Alternator output 14.63v. At battery 14.60v. On disconnecting negative terminal with engine running, the battery light is not coming on. All bulbs pass the test.

 

Typo for 0.03V

But... don't disconnect the battery. It's needed for smoothing the power.

 

I only disconnected the negative terminal to see if the battery light would come on to register a no charge. It made no difference.

 

That counts as disconnecting. Not good for modern cars.

 

+1 on that. Hopefully no damage occured, but disconnecting the battery with the engine running can cause huge voltage spikes.

Did you ever try externally charging the battery, as previously suggested? May seem like a waste of time, but it's one of the preliminary steps for any electrical troubleshooting.

This thread is getting a bit convoluted, but is your only present issue that the battery light doesn't seem to be behaving properly? If so, on a cost/benefit scale, I'd be tempted to just live with it. Test the charging system again to be sure the battery disconnect didn't cause any damage.

Then get a little voltmeter doohickey that plugs into the cigarette lighter. This lets you keep an eye on the charging system much more effectively than a little red light that comes on way too late. The doohickey in my car has a warning chime that sounds for low voltage, so you don't constantly have to monitor it.

 

Did recharge on battery for 12hrs with charger set to 10 amps as suggested, Has made no difference. Rechecked complete system and thankfully no damaged has occurred by disconnecting battery, Alternator output remains stable at 14.6 volts. Thanks all for advice