Hi all, I'm wondering if there are any "usual suspects" that would drain the battery in a day or two.. (fwiw, the battery is new this year, January 2018)

1998 F-150 (XLT), 4.2L, 2wd, 202,000 miles...

The roof has some rust, and there's a little leakage above the rear window.

Yesterday I tried to find the short with a multi-meter, with the negative cable disconnected and the multi-meter clamped between the terminal and the clamp...

It only showed ".13" milli-amps, which doesn't make any sense to me. Maybe I was doing it wrong? I never did this test before, so I was going by a vid that I found on youtube... iirc, the vid said 30-50 milli-amps is normal, but I was only seeing ".13" ...

When I started the test, the battery showed about 11.9 V at the terminals (with the engine off). It took a couple hours (on a charger) to get it charged up to 12.4 V so I could begin the test.

Even though ".13" looked wrong, I still went ahead and pulled all the fuses in the box under the hood, while watching for a drop on the multi-meter, but there was no change.

I didn't check every single fuse under the dash, but the few I did check didn't make any change either.

Last night, the battery was charged up to 12.43 V...
Today, it's was down to 11.85 V at the terminals.
She still fired right up, and the battery shows 13.9 V while idling.

I don't know what to check next, any suggestions would be much appreciated!

Thanks in advance,

Jim

 

ps: a couple more details...

I just left the truck running for about 20 minutes, and the battery is already up to 12.51 V... yesterday it took a long time just to get to 12.4 V, but it was a little wetter yesterday. Today is nice and dry.

The horn fuse and relay have been removed a couple months ago because the horn was going off by itself. I don't see how that would matter, but it's a detail nonetheless.

I checked the water in the battery yesterday, and it's full.

 

1. Could it be 0.13 A? Is the battery healthy?
2. The horn in my 97 had the same problem. Culprit was the horn pad that got stuck closed.
3. Get wiring diagrams. You will need them

 

https://www.ford-trucks.com/forums/1...overnight.html

 

Thanks for the link Steve, I'll take a closer look at that "Battery saver relay" and fuse.. I don't think I pulled that fuse when I was testing yesterday.. But I did unplug the hood light, and I clicked the door latch to turn off the interior lights while checking the under-dash fuses too...

I'm wondering if I did something wrong when I connected the multi-meter. Or maybe the meter is fried? It seems to work fine for measuring volts at the battery, but it only showed ".13" milliamps when I hooked it up between the negative cable and the negative post of the battery.

 

Thanks paker,

The battery is "new" as of January '18, and it's full of water. So I'm assuming it's good, but I dunno for sure.

About your 3 points;

1- It very well could be ".13 Amps"... I don't fully understand all the features on the multi-meter, so maybe I didn't set it right. Or maybe something is burned out on it... but that sounds more like the draw that must be happening. (The multi-meter does have a new battery in it, but I'm still not sure if I trust it)..

2- When I had the problem with the horn going off, I read a thread about how the airbag swells up with time, and it presses on the horn switch by itself. That makes sense to me because some of the seams are splitting around the steering wheel on mine. ...I pulled the horn fuse months ago, to shut the horn off...

And then, a couple weeks ago, I wound up using the horn relay as a fuel pump relay (it's the same part), and it fixed the problem with the fuel pressure.

So, basically, my horn is thoroughly unplugged. Both locations are empty of fuse and relay now.

3- YES! I agree! Do you know where I can find wiring diagrams online?


Thanks again

 

 

In your first post you said.......charged up to 12.43.....overnight down to 11.85 then13.9 running.
This tells me the Alternator is able to charge,,,,however,,,, if the Alternator Diode stack is leaky it will discharge the battery because it has one side connected to it's frame and ground.
Since this dissipates power in the form of heat it may feel a bit warm compared to other parts.
To check this out remove the heavy lead from the Alternator carefully then retouch it back on the terminal.
If you see any spark at all the Diodes are faulty.
Or you could measure any current with the right meter because you don't know how much might flow and burn the meter.
Easier to look for the signs of a spark.
Again, the Alternator will work but cause a discharge from the fault.
This will not show up as a charge lamp indicator fault.
Good luck.

 

Thanks again Bluegrass 7,

When I first read your comment on the thread that Steve re-posted above, I didn't quite understand it.

I never heard of the "Alternator Diode stack", so I had to google it. But anyways...

I guess you're saying I should unbolt the big red wire in this pic? Then tap it on the post to see if it sparks?... I hope that doesn't sound like a stupid question, but electricity is magic to me... I don't understand too much about it, and I don't want to mess anything up.



The engine was still warm when I took that pic, so I couldn't really check for heat right now..

In that pic above, it "looks" like the yellow/black wire is shorting on the alt, but it's not. It's just the angle...
It's not actually touching at all, and the crusty looking part rubbed right off. The sheathing is still intact.

Thanks again man,

Jim

 

Thanks Jim,

iirc, I started with the red lead in the 10A jack at first... But I'm pretty sure I moved it to the regular jack and put it into the ~mA range before I started pulling fuses for testing...

The vid I was going by said that 30-50 mA was normal, that's why I don't understand the reading of ".13" mA.

I went forward with the testing anyway, thinking that maybe the decimal was off by a couple spaces, but I dunno... I'll have to try it again, unless Bluegrass' method (above) finds the short.

When I put a new battery in the multi-meter, I didn't see a fuse in there. But I never did open the casing yet.

And yeah, I didn't wait the 45 minutes for everything to go into "sleep" mode either.. I was assuming that 1998 ain't "that" modern... I don't have keyless entry or anything like that..

fwiw, here's the vid I was going by.

Thanks again,

Jim

 

Meter current readings.
1Amp = 1000 milliamps. (Ma).
.13 amp = 130 ma.
Normal resting current draw assuming the modules go onto sleep mode would be from the computer memory and radio programming memory.
This current would be in the 45 to 60 ma range +\-. Or .045 to .060 amp.
It's just a matter of moving the decimal point and changing the designation.

 

Thanks Bluegrass, I understand that part..

But let me ask again, to test the diode stack, you're talking about unbolting that big red wire on back of the alternator, correct?

 

Well, thanks again Bluegrass 7.. I finally did your test this afternoon, but there was no sparks at that post...

The battery was showing 12.05 V at the terminals before I started.

I don't know what to check next, but my suspicion is that I might find something above the headliner since the roof leaks a little. But I dunno. I'd rather find a way to test it before I start ripping everything apart..

 

I would start all over again and check the charging system for operation.
Get your voltmeter connected to the battery terminals.
Crank the engine, start, then look at the voltmeter reading.
It should be at least 15 volts or more depending on battery health and state of charge before cranking.
If the voltage is up, the Alternator is outputting normal and should drop down after a few minutes or more as the battery recovers it's charge..
Let the motor run until the voltage has come down to 14 +/- a tenth or so. this eliminate a charge issue but not necessarily a discharge issue.
Pull the under hood lamp, let the truck set off an hour.
Then check the drain again to see what you have.
If over the normal range, something either has not gone into sleep mode or is faulty or even a relay that has contacts burnt together like the fuel pump etc...
Look at your owner manual for fuse assignments and pull the ones that deal with modules like the Radio, Gem, etc to see if any drop the drain back to the normal range.
If you pull the computer memory fuse or disconnect the battery for any reason it puts the computer into full self diagnostic mode until all is completed.
A drain much above several hundred milliamps won't drain a fully charged battery for quite some time if the battery is in good health and it's state of charges was up.
After all the battery has to supply more than 100 AMPS to crank the motor.
Big difference between several hundred milliamps and 100 amps for discharge time...

 

Thanks again man...

Right now, I have the battery disconnected, hood up with the light unplugged, door open but latch activated (to turn off dome lights), and I'm letting it sit. It's been sitting about 15-20 minutes now...

Right after my previous post, I left it idling for 25 minutes. The battery charged up to 12.4 V in that time (up from 12.05).

On my multi-meter, it shows zeros when I use the 10amp jack... But in the other jack, it shows "0.13 mA"...

So once again, I went with it... and this time I checked every single fuse and relay under the dash. Nothing made it drop, although it did go up to 0.14 mA a couple times (just for a second).

Last week when I tried it, I checked every fuse under the hood but not every one under the dash. Today I checked everything under the dash... still nothing...

So I'm letting it sit right now, and I'll try the test again after she sits for a while.

Thanks again Bluegrass, I appreciate all your advice with this.