Ford F150 2002 drains battery overnight, new alternator and battery, no change. Alternator charges ok, and will restart throught the day, but when left overnight, will not start.

It would seem as though you have a drain somewhere in the electrical system.

A faulty alternator can cause a battery to drain - sometimes - within minutes. It's the rectifier pack - the diodes in the back of the alternator which burn out.

Charge your battery and when parked up, disconnect the connector at the rear of the alternator. If the vehicle cranks ok the next morning you have to suspect the alternator.

If the problem persists you then obviously have a current drain somewhere else. As you have removed the fuses and it made no difference .. this suggest that the drain could be in the instrument cluster/dashboard.

The best option is to visit an auto electrician. He'll be able to identify the cause of the drain within minutes

The alarm light will not kill the battery. Your diode in the alternator may be bad. This will slowly drain the battery. Replace the alternator. Or charge it up and go to auto parts store and have them test the battery and alternator and starter.

if you installed a new battery as well as a new alternator, it should not go dead overnight. if you have a short in the vehicle that will drain a new battery that rapidly, the cable would have been melted already. although, dome lights do have a tendency to drain batteries, but not overnight. use a multimeter to check the battery voltage while the motor is running. it should read above 13 volts DC signifying that the alternator is indeed charging the battery.

This problem may be a drain or a bad battery or alternator.

The first thing to do before going on trying to find the system that is draining the battery would be to have the battery tested and charging system tested.

A weak battery will seem ok after the car is jumped or will barely start the car and the alternator will charge it even though the alternator is overworking due to weak battery and during the day or when car does not sit long it will seem ok. then when car sits overnight or a few days battery will weaken on its own, making it look like a drain,

so first step is battery test and alternator/charging system test.

You would have checked the charging system before replacing the alternator, so I will assume the charging system is good.
If the battery is being discharged overnight or over a few days, you would need to disconnect it and check every circuit on the truck to find the drain.

Sounds like a bad alternator. Drained your battery and when you turned on the lights it took all the power left in your battery. When you drain a battery down that far, they are real hard to jump, and coupled with the alternator, the car is not producing enough current to start and stay running.

I would take the alternator off and take it to oyur local auto parts store to be tested. If bad, replace it and charge the battery fully before starting. Then check voltage at battery with motor running. Should be 13.2 -14 Volts DC. If not, you may have a bad battery cable or blown fusible link. (especially that if the alternator tests good).....Mike

nancycmixon, When you see this "check your charging system" you need to have the alternator checked. This is the main component for the charging system. A normal alternator will put out 13.6 to 14.6 volts. A few tenths of a volt either way won't mean too much but if they are extremely over or under these values means you have a bad alternator. I believe that your vehicle has a voltage meter in the dashboard and it will usually read in the thirteen to fourteen volts range. As far as your battery losing its charge overnight means that you have another problem and that is you have what is called a parasitic drain. There are a certain amount of parasitic drains already in the car with the radio memory and maybe a clock that constantly displays the time and the antitheft system in the car. These will not drain your battery overnight. You have something else draining your battery that is your problem. Have the alternator checked and mention the battery drain. There is test for this but it is too lengthy to post here. Sorry about that. Good luck with this.

Have your alternator and voltage regulator checked. I once had a galaxie 500 that did the same thing - turned out the alternator was bad and the regulator drained the battery overnight. I changed out both and problem solved - hope you have the same luck!!!

Could be, have the battery LOAD TESTED and also verify that the alternator and the connections are good.

POWER DOOR LOCKS / STARTER SOLENOID CONTACTS SHORT /A BAD ALTERNATOR REGULATOR.AC AND HEATER BLOWER RELAY STUCK CLOSE.ALL THESE THING CAN CAUSE BATTERY DRAIN.