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Ford F150 Elictrical Problem

I have a 1999 F-150 4.6L V-8, and the battery light is staying on. Something is draining the battery. I have taken it to Auto Zone, and they tested the battery (brand new), starter, and alternator - all show good. The only error they can register is “C1226 brake light lamp short.” What could be causing this? I had to get jump started at a gas station 2 nights ago. I have checked the alternator fuse, and it is ok. Could the wiring be bad somewhere?
Thanks for the help!

Is there a voltmeter in the dash? If so what is the voltage when the engine is running at 1500 rpm? The voltage should read approximately 14.5v at fast idle and 12.6v with the key on and the engine not running. And with the AC/heater fan on high, headlights and wipers also on the voltage should remain above 13v at fast idle.

Auto Zone and the other McParts stores wishe they could come up with a simple “idiot proof” tester for the charging/starting system but they haven’t quite worked out all the issues.

I do not have a voltmeter. All I have is the hand that shows low to high battery charging, and it stays right in the middle at all times. Autozone replaced my battery today as it was only two months old, but that was not the issue. Any ideas how to correct it?

Since AutoZone tested the battery and alternator, for now at least assume those are ok.

You may have a short that is draining the battery all the time, even when the engine is turned off. You’ve looked at all the lights, including the rear brake lights, right? None of them are on? And they all work correctly and are on when they are supposed to be on? The brake lights, the tail lights, the blinkers, the side lights? Front and back? All the lights are working correctly?

If all that checks out ok, I’d still go with the C1226 code, and expect there is still a short in the tail light circuit. It’s just not bad enough to stop the lights from appearing to work. So look around those brake light fixtures in the rear, see if you notice anything unusual, corrosions, dents, something loose. If you’ve ever had a collision in that area, of course that’s the first place to look. You may need to take the tail light assembly partially apart to see what’s happening on the inside, and to see the connectors. And look at the wiring as it approaches the tail light, esp if it might have been pinched in the tailgate.

Still can’t see anything? You could pull the fuse for the brake lights and let it remain out overnight, see if that has any effect on the ability to crank the engine the next day. If it helps, you know that is the circuit doing the draining. Be sure to put the fuse back in of course before driving. Otherwise you won’t have any brake lights.

Most shops would have someone who could do the measurement to verify you have a phantom battery drain and confirm which circuit it is, without much expense. It just involves working at the battery, nothing else. Asking them to find exactly where the short is and fix it might be a little more expensive.

Here’s an idea, sort of off in left center field, but you might try just to see what happens. When current flows in a wire, it creates a magnetic field around that wire. You can’t see the magnetic field, but it will show up as a needle deflection if you hold a magnetic compass (like boy scouts would use to find north) near the wire. In theory at least you could start at the battery and follow the magnetic field to the point it disappears, then you’d know where the short was. Unless you have a lot more time than money though, probably the most economical thing is to let a shop at least determine what the problem is. Then you have the option to fix it yourself or not. Best of luck.

When the battery warning light is on it usually means that the alternator isn’t charging the battery as well as it should be. This could be due to a wiring problem within the car since the battery and alternator checked okay. Check the voltage getting to the battery while the engine is running around 1,500 RPM. You should see between 13.5 and 14.8 volts DC. Check for AC ripple voltage also. That should be less than .1 volt AC. Make sure the meter blocks the DC voltage component when you do that test. To see if it does check the battery voltage in the AC voltage mode while the engine is off. If the meter shows zero voltage after a little bit you are good to go. If it doesn’t then you need to put a capacitor in series with one of the meter leads. Try a .5 microfarad.

In most cases, current drain on the battery while parked should be less than 30 milliamps after systems have gone into the sleep mode.