Battery drain

Did you pull the fuse for the windows and radio? Did it make any change on the draw?

I want you to follow the following directions for checking draw and let me know what you find.

https://www.2carpros.com/first_things/why_is_my_car_battery_dead_over_night.htm

Let me know.

Joe

Try an ammeter

Do the battery drain test below:

https://www.2carpros.com/articles/car-battery-dead-overnight

The first thing is to have the battery tested. Everything you described is typical of a battery with a shorted cell. You can start the diagnosis by measuring its voltage with the engine not running. If it's good and fully-charged, it will be at 12.6 volts. If you find it's closer to 12.2 volts, it's good but discharged. Charge it at a slow rate for an hour. If you find it to be around 11 volts, it has a shorted cell and must be replaced.

I'm afraid I don't have a real good answer. You might be hearing something being run by the Engine Computer for a self-test that is performed when the engine is stopped. You might inquire at a Ford dealership, otherwise someone is going to have to figure out exactly what it is you're hearing so we can determine what is happening.

It can be a little tricky with all the computers on the truck. Some of them can draw a high current for up to 20 minutes until they go to "sleep" mode. Anything you do to momentarily break the circuit starts that 20 minute wait period all over. That includes switching the range on your ammeter. If you start out on a higher scale you won't get the necessary accuracy. If you start out on a lower scale you can pop the meter's internal fuse. On top of that, some computers can lock up after the battery is reconnected but that doesn't seem to be a big Ford problem and that wasn't real common yet in 2003.

The secret is to disconnect one battery cable to insert your ammeter AND connect a jumper wire across the meter to in effect short it out. Some computers might "wake up" so let the meter and jumper sit there for at least 20 minutes, then remove the jumper wire. All current will go through the ammeter so it can be measured. If you need to switch to a lower scale, put the jumper wire back in place first, switch the meter, then remove the jumper again.

Unless the manufacturer specifies differently, the industry-accepted maximum is 35 milliamps to maintain the memory circuits in the radio and computers. At that rate a good battery will still start the engine after sitting for three weeks. Slightly more than that won't kill the battery overnight but you don't want to see 200 milliamps or more.

Typically when there is a drain, it's really a drain. You won't have to guess. You'll likely find an amp or more, especially if the battery goes dead overnight. Remove one fuse at a time to see if one makes the current drop to an acceptable level. That fuse's function will give you an idea of which component to look at. Don't forget that if you open the doors, the interior lights will turn on. You will also want to disconnect an under-hood light.

Before you go through all this work, it would make sense to be sure the generator is recharging the battery after you start the engine. Use a voltmeter to measure battery voltage. A fully charged good battery will measure close to 12.6 volts. If you charge it with a battery charger, then let it sit overnight and it holds a charge, suspect the generator, not a drain. If you find closer to 12.0 volts, the battery is good but discharged.

Remeasure the battery voltage when the engine is running. It must be between 13.75 and 14.75 volts. If it is low, again, suspect the generator.

Battery drain test