The battery light is on in my dash. To test it I probed the car battery with a multimeter. Car off the battery reads 12.5 volts. With the car running and no headlights on, heater fan off, etc the meter reads 15-15.5volts. When I turn everything electrical I can think of on the meter reads 14-14.5volts. Is this normal or is the second scenario overcharging the battery? What else can I test that may be keeping the battery light on in the dash?

 

What year, model, truck are you working on?

 

98 lincoln navigator

 

Bad alternator probably.

 

The 15.5v reading that I was first getting while idling with no accessories on must have been a fluke. Read the meter yesterday with her in idle, no accessories and it hit 14.5v. Accessories on she hit 14.5v. Driving down the road about a mile the dash light went off. Not sure what tripped it in the first place but there doesn't seem to be an issue.

 

I had a voltage regulator go bad and two things I experianced. One was my battery kept going dead over night for no reason. My amp gauge was reading 45 Amps when running (70 amp alternator) and when I checked the battery with the key off the battery had 15.5 volts. With car running the alternator was putting out 15 volts. Truth is an alternator is supposed to put out slightly higher voltage than battery voltage but vary amperage to charge the battery and keep your system going. Battery voltage is 12.7 for a new battery or a fully charged battery. Every charging system Ive seen working properly runs at 14 volts with engine running. Some vehicles might be different but all the ones ive seen never went over 14 volts when working properly.

I know your problem is resolved now but if your battery starts going dead over night and you have nothing on to cause it then I would check your regulator if you have an external regulator otherwise time to get a new alternator.

 

I know the problem is solved, but 15VDC may not be a fluke. The voltage regulator could be going bad and putting that much voltage out. If it is going bad, that 15VDC may not be the output at all times.

A good alt / volt regulator will put 14.2 to 14.5 out at all times, load or not. Just keep a check on it.