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drain on Ford F150's new battery?
December 19, 2009 11:27 AM   Subscribe

Help us diagnose our Ford F150: what could be draining down the (new) battery overnight? We're suddenly seeing apparent battery drainage in our pickup truck, a 1994 Ford F150. Though the truck starts up fine, the dashboard battery gauge reads low immediately upon ignition, the windshield wipers are sluggish, and the dashboard lights are dim. We thought the old battery was likely dying, so we had it replaced with a new battery... but that hasn't solved the problem.

(I'm posting this for my husband, who drives the truck. Here is the problem in his words.)
It's a 1994 Ford F150 pickup. Two days ago, the battery light came on and the battery gauge on the dash was at the low end of the meter when I started the truck after work (it had been sitting for about 9 hours). I assumed it was a bad battery, so I had the battery replaced at a chain auto place.

Everything seemed fine until I got out of work that night (after the truck had been sitting for about 9 hours) and the problem was exactly the same. The alternator seems to be working, as the battery gauge goes up to where it belongs if I let the truck run for about 20 minutes. There are no lights left on (glovebox, dome light, etc). It seems that, when the truck is off, something is drawing power from the battery.

When the gauge is low, the dash lights dim, and the windshield wipers are slow and sluggish. When it's charged back up, everything is normal again.

While I'm letting the truck idle to charge up the battery, the gauge will go up slightly if I rev the engine, but goes back down when I take my foot off the gas. Once it's fully charged again, revving the engine has no effect.

Both before and after getting the battery replaced, the truck started up just fine (no problem at all), even though the battery light came on and the battery gauge was low.

Once the battery is charged up again, turning the truck off for ten minutes-a half hour has no effect; the battery is still charged normally after that length of time.
We'll be taking it in to the mechanic on Monday, but with holiday errands and visits pressing, we'd love to get a headstart on the diagnostics over the weekend.

Some specific questions

1. Aside from the things we've checked (dome light, glovebox light, ashtray light, radio), what could be draining down the battery while the truck is off? Especially, do you know of any idiosyncratic drainage problems with the Ford F150? (We're also checking the forums on a Ford-specific board, but any hints would be helpful.)

2. Are there any simple home diagnostic tests we could make? Again, anything specific to the Ford F150 would be useful, but not necessary.

The fact that the truck starts normally (that is, readily and vigorously) seems to make this a different question than previous AskMe questions (which all seem to include a car that won't turn over) about a drained battery or dying alternator... or am I wrong? If the alternator is faulty, would the car be starting normally?
posted by Elsa to Travel & Transportation (28 answers total)
 
Could it be the cold? Have you tried plugging it in overnight?
posted by Sys Rq at 11:31 AM on December 19, 2009


If your brake fluid is low it might have the brake pedal so low the lights are on.
Would you have noticed that?
posted by Iron Rat at 11:31 AM on December 19, 2009


The battery gauge is not really a battery gauge -- it just has a picture of a battery on it because that's the icon that people associate with the electrical system. It's a voltmeter. If it's ever reading low while the engine is running, then your charging system isn't working correctly. It sounds as if there's an intermittent fault that improves as the temperature rises (engine warms up). Whether that fault is in the alternator, voltage regulator (which could be integral to the alternator) or a loose / corroded cable is up to your mechanic to figure out.
posted by jon1270 at 11:35 AM on December 19, 2009


And also -- do you hear any belts squealing? The alternator belt could be slipping.
posted by jon1270 at 11:37 AM on December 19, 2009


My recall on Ford trucks is low, but I remember that on my Ford vehicles years ago, the regulator and the alternator were separate parts. If one or the other is out, that can cause the battery to drain or not charge efficiently.

I don't think it's outside the realm of possibility that the alt/reg could be bad and still let the truck start.
posted by lysdexic at 11:40 AM on December 19, 2009


If the alternator is faulty but the battery is charged, it would start up normally. However, since it starts, it's likely not an alternator.

You may have some sort of vampire that is going to be impossible to diagnose over the internet if nothing is visibly 'on'. Also, you've probably checked this, but sometimes cigarette lighter chargers stay on when the car turns off.

My husband had a Fury that if the passenger door was shut while the window was down he'd come out to a dead battery in the morning. The culprit? A slightly-exposed brake light wire.
posted by bookdragoness at 11:41 AM on December 19, 2009


The alternator won't directly affect the way the truck starts -- all the starting current comes from the battery. (But if the alternator's dying then it won't charge the battery up, so starting would become a problem, of course.)

I'd try disconnecting the battery after you stop the engine, to see if the battery is faulty (and draining itself internally) or not. Actually, my first step would be to put a current meter between the battery and one of it's connectors, while everything is turned off, so determining if there's a drain -- but you may not have a suitable meter, so use the disconnection method. When you want to drive again reconnect the battery and check if the gauge reads low: if it does, then the battery is faulty.

If the battery is good but there is an electric drain with everything turned off then you'll probably need professional help to find it, unfortunately.
posted by anadem at 11:43 AM on December 19, 2009


However, since it starts, it's likely not an alternator

This is wrong. The battery starts the car, not the alternator. You could take the alternator out and throw it in the ditch, and the car would still start.
posted by jon1270 at 11:43 AM on December 19, 2009


[Since my husband, the only one who drives the truck, is at work today, I'll be relaying suggestions to him later today and then relaying his responses. These suggestions are all helpful --- thanks and keep 'em coming!]
posted by Elsa at 11:43 AM on December 19, 2009


I had this (or a very similar) problem in a Corolla once, and it was the alternator. The new battery makes things seem fine for a while, but because it's not being recharged while driving, it eventually gives out.
posted by rhizome at 12:21 PM on December 19, 2009


Put a DC ammeter in series with the positive battery cable. With the ignition off, look for a reading. A drain reading in the milli amp range is usually acceptable. If you get a large reading, pull the fuses one at a time until you see the amperage drop. This will show you which branch circuit in the truck wiring may have a problem. Do not start the car without removing the meter.
posted by Raybun at 12:26 PM on December 19, 2009 [1 favorite]


Not too long ago, the battery on my wife's car went out. I replaced with one from a big chain, but then a week later it started having problems again. It turned out that I had gotten a bad battery from the store, which happens occasionally. Most auto stores will test the battery for free, especially if you bought it there - might be worth a shot.
posted by chrisamiller at 12:41 PM on December 19, 2009


Put a voltmeter across the battery terminals when the truck is running. It should read about 14 to 14.5 volts if your alternator is charging properly. If not, the first thing you replace is the alternator brushes/diode unit (cheap), then maybe the alternator itself.
posted by weapons-grade pandemonium at 1:01 PM on December 19, 2009 [1 favorite]


My bet is alternator. If there are AutoZone stores in your area, take the truck over there and they can run a fairly quick, free (at least here in Texas it's free) test that will tell you if the alternator is bad. If your hubby will be changing out the alternator himself, he can rent* any special tools needed to change it out and their website has directions on how to do it.

*Rent is free, but you pay for the tool up front, then they return the full price you paid when the tool is returned.
posted by Doohickie at 1:58 PM on December 19, 2009 [1 favorite]


You need a new alternator.

A healthy battery will have enough power to crank the engine over. Once the engine is running, the alternator creates the energy necessary to run the car. Well, the systems in the car only require 12v to operate, but the alternator should put out 13.5-15V in order to charge up the battery. If the car starts normally, you do NOT need a new battery.

With the car running, a voltmeter should measure those 13.5-15V across the positive and negative terminals of the battery. If not, install a new alternator. I wouldn't bother rebuilding the one you have. It's just as cheap and easy to nail a new one in.

If my memory is correct, the alternator is readily accessible on your F-150. With a few basic tools, you could replace it yourselves. Disconnect the battery negative cable, remove the accessory belt, and I think all you need is a 13mm socket or wrench and the alternator should come right out. Just make sure that you buy one that comes with a new pulley installed since it's kind of annoying to swap them over.
posted by Jon-o at 2:13 PM on December 19, 2009 [1 favorite]


With the car running, a voltmeter should measure those 13.5-15V across the positive and negative terminals of the battery. If not, install a new alternator.

You might want to take a good look at the wiring before replacing the alternator if voltage across the battery is low: I once had a similar problem (in a completely different car) due to a loose connection along the path from the negative terminal to ground. Once we figured out what it was, it took about five minutes to replace a faulty clip.
posted by Dr Dracator at 4:14 PM on December 19, 2009


Check the brushes first. The alternator brushes are two spring-loaded carbon bars that wear down with use. The unit, about the size of a cigarette lighter, will come out with one or two screws. If this is the problem, they'll probably cost you fifteen bucks and your alternator will charge like new.
posted by weapons-grade pandemonium at 4:17 PM on December 19, 2009


My husband has a Ford F-150 of about the same year. He does most of the maintenance & repairs on it and our other four vehicles. He said that it's most likely a short in the truck's wiring somewhere -- where something has rubbed off the coating on wiring, and it's draining the battery. To preserve the battery until you get it to a mechanic, you could disconnect the positive battery cable when you're going to leave it sitting for awhile, then connect it again when you're ready to leave.

He said it's definitely not the alternator since the battery does fully charge after you've started it. To find out whether or not your problem is a bad alternator, start the vehicle, disconnect the positive battery cable, and if the truck dies, it means your alternator is bad. The battery starts the car, and then the alternator charges the battery back up. The alternator also runs the lights, wipers, radio, sparks the spark plugs, and so on while your car is running. If your alternator is bad and therefore can no longer run those things, the battery will run them until it's drained, then the vehicle will die.
posted by onemorething at 5:23 PM on December 19, 2009


If your battery was discharging due to a hard short, I think the symptom that would get your attention would be the blow fuse (or the fire).

I'm guessing your alternator isn't fully charging the battery and if you do put a volt meter across the two terminals you'll get something barely sufficient.

Before I replaced it, I'd check and make sure the battery connections are tight on both ends, the big wire on the alternator is tight, and the then unplug and plug in the little wire on the alternator (which powers the coil, making it a magnet for that generating electricity thing). If any of these (plus a few others in there) are making poor connections then you're not going to be charging very efficiently.
posted by Kid Charlemagne at 6:14 PM on December 19, 2009


My 1997 Ford Taurus had a sort of similar problem.
One day, the battery was just completely dead. I bought a new one, and a couple days later... same thing. Dead. Autozone tested the alternator, it was fine. Tested the battery, as well. Also fine. Installed a quick disconnect on the battery, as we had deduced something was perpetually on and pulling power.
I thought about what had changed about my car recently.. obvious, little things, you know?
Everyone laughed at me, but I suspected that my problem had something to do with the tape I'd recently gotten stuck in the tape deck.
A few months later, I was very sick of disconnecting the battery every damn time I got out of the car.
I'd tried before, but this time I was determined.
I got some hemostats and pulled the tape out, and stopped using the quick disconnect to see what would happen.
The battery stayed charged, and I never used the quick disconnect again.
posted by defragmeout at 6:40 PM on December 19, 2009


To (slowly) diagnose the problem, ensure the battery is charged, and then start pulling fuses out, one at a time. Pull one fuse out, let it sit overnight. If it starts in the morning, then you know which circuit is draining the battery. If it doesn't start, replace the fuse, and try removing another one (after re-charging, obviously). Keep at it until you find the culprit circuit.

If you don't have a battery charger, you can recharge the battery by jump-starting the truck and letting it run for about 15-minutes. If your battery doesn't recharge in that time while running, you'll need a new battery.

It may take a week or two, but eventually you'll know which circuit is draining the battery, and will get you pointed in the right direction.

Also be sure that all battery connections are clean with no corrosion. Also inspect the cables that go from the battery to the starter and the ground cable that attaches to the body and insure that there are in decent shape. Especially that ground cable.


I was a mechanic for 15 years and "weird" electrical problems are the worst thing I have ever had to deal with.

Silly things to check that I have seen:

-Make sure there isn't a coin (or other conductible object) stuck in the cigarette lighter.

-If it is a truck, you may have a trailer-light harness. These tend to cause problems as they age.

-Any aftermarket things hooked up (stereo gear, extra horns, CB, etc), disconnect them as well, like pulling a fuse one at a time as I suggested above. If there are accessories such as these, start with them FIRST.

-Make sure there isn't an alien living near the truck. They tend to such energy out of car batteries.

Good Luck.
posted by peewinkle at 7:20 PM on December 19, 2009 [1 favorite]


* replace each fuse that you remove before you try starting the truck in the morning
posted by peewinkle at 7:22 PM on December 19, 2009


Oh, and the other thing to try is changing the "relay", which should be on the passenger side under the hood just above/near the wheel well. They are known to go bad, and aren't very expensive to replace. It's a little black thing with between 4-6 wires attached to it, one wire from the battery.
posted by peewinkle at 7:28 PM on December 19, 2009


oh, and yes, check the alternator first. Above advice is good. I'm just thinking what to do if the alternator is in good shape.
posted by peewinkle at 7:30 PM on December 19, 2009


Doohickie: "... If there are AutoZone stores in your area, take the truck over there and they can run a fairly quick, free (at least here in Texas it's free) test that will tell you if the alternator is bad. If your hubby will be changing out the alternator himself, he can rent* any special tools needed to change it out and their website has directions on how to do it..."

I came in here to say "Get thee to AutoZone" as they will test the electrical system, free, and while they're not always rocket scientists they often could be, often the guys (and/or gals) working there have worked as mechanics. They will print out the instructions to any job you're going to do on your vehicle, and give you any tips they know of for your particular vehicle or just in general. The point is that they really want to help you, and will -- I've had great luck with them.

I've replaced an alternator (or two) on my 1994 F150 (190,000 miles so far, shooting for 250,000, or more...) and it's a piece of cake for anyone who can spin a wrench even a little bit. And while they're not 'supposed' to let you do any work in their parking lot I've done complete brake jobs behind various AutoZone stores both on this pickup and on the Ford pickup I owned prior to this one, I've replaced shocks, I've rebuilt this and/or that, never anything as much as a clutch but I hire that out anyways or I would do it there, I just don't have the jack for that plus it's a bit out of my comfort zone anymore (I'm aged and stuff). The people there will usually even come out and show you this or that, I've had guys grab a wrench or two a time or two but that's just good luck, and fun, too.

Sears also will run an electrical test on your vehicle (if you're maybe more comfortable with Sears for whatever reason; I'm perfectly comfortable with the help I've gotten from the people working at AutoZone); they'll charge you for the test but will refund the charge if they do the work and/or replace the battery, if that is what is needed.


peewinkle: "To (slowly) diagnose the problem ..."

Every word peewinkle says is gospel, I hit the fave button as hard as I could.
posted by dancestoblue at 8:55 PM on December 19, 2009


I may not be the best mechanic, but I would suggest disconnecting the battery when you park it. If it starts just fine when you reconnect it in the morning, then you know you have a drain that is occurring in the night.
posted by Megafly at 11:13 PM on December 19, 2009


Thanks, everyone! It looks like our first stop today is the local Autozone, to see if they can test the electrical system.
posted by Elsa at 7:33 AM on December 20, 2009


AutoZone has diagnosed it as a faulty alternator. Since we're apartment-dwellers (with no garage or parking area or other enclosed workspace), we'll be taking it in to our mechanic after all, rather than trying to tackle the problem in the snowy streets. At least we have an idea what the problem is!

Thanks again for all the hints and help --- we had zero experience with AutoZone and probably wouldn't have thought of turning to them. Good to know they're handy and helpful! ... like AskMe itself. Thanks!
posted by Elsa at 11:42 AM on December 20, 2009


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