Hey everyone. I found an old thread on here with electrical problems. it was an old one, but the responses and help were incredible. this looks like an awesome site.
I recently got a 99 f150. the brake lights do not work (blinkers and tail lights work fine) and the battery is draining. I do not know yet if the 2 issues are related. please bare with me on the lack of information, i just got the truck to the house last night.
I believe it is taking 2-3 days to drain down, but that is just what i was told, i have not verified that yet. I do know that when i picked it up, it was dead. When i got it home, i checked the obvious things.. dash lights staying on, glove box light, hood light etc. I didnt see anything on.
The only other thing i did last night was put a volt meter on the battery. I unhooked the negative battery lead and put a voltmeter on the negative post and the negative lead. it showed 22 volts on the neg and 24 on the pos (pos was still hooked up). I can work on the mechanics of the truck, but am fairly new to the electrical side. shouldnt there be 0 volts on the neg side??
thank you all in advance. I plan to do some digging on it this evening and really dive in tomorrow and saturday. My plan of action right now is to get the voltmeter on the disconnected neg side of the battery and start pulling fuses to see if i can isolate where the problem is. from my research, my suspicion is leaning towards the multi function switch.. possibly a wire came loose and is grounding out.. I will update as i go along. Thanks!

 

I can tell you right away that you did not see 22 or 24 volts.
The max voltage you could ever see is about 16 volts from the alternator running full output due to a faulty regulator.
Even at 16 volts nearly every light on the truck is subject to blow in short order, not to mention possible computer damage.
You need to begin checking for shorted Diodes in the alternator.
This condition will still output and charge the battery but cause a drain after shutdown.
Best safe way it get a look at drain levels it with a low wattage interior 12 volt lamp in series with one of the battery leads. It should light. Then open circuits until it goes dim or out. Investigate to see what is on that circuit by consulting the Owner manual for fuse assignments.
As Charlie Chan would say... use head first, hands second.
Good luck.

 

Blue grass-
Thank you for your reply. Perhaps i had the voltmeter on a wrong setting or something, because it did indeed show 22 and 24. i will check again this evening.
thank your for your suggestions, i will try it out.

 

So what you accomplished is putting the parasitic amperage draw through your volt meter. I don't know if that cooked your meter or not.

But if you set your meter up to read amperage and do the same thing, you would actually be measuring the amp drain on the battery. (Start out with your meter on the 10 amp scale so you don't blow the fuse in the amp side of your meter. If the draw is less than the next lower scale on your amp meter, drop down to the next lower amp range.)

After all the computer modules go to sleep (could take up to 40+ minutes) you would like to see a draw of less than ~50 miliamps.

 

pdqford-
My meter is still functional. So the volts doesnt matter, what i need to be looking at is amps from what i understand from your post. once i hook up the meter, i will start pulling fuses and try to find out where the power is drawing from. does that sound like the best way to start to you?
Thank you

 

Yep. But be sure you have an excessive draw first.
(No sense in looking for a problem if it's not there ;-)

 

I will check for a draw of more than 50 milliamps before i start digging through the fuses. I will be home soon and have an update later this evening.
Thank you pdqford

 

Ok, so i have been working on the truck this morning and am having some problems.
Bluegrass- you were correct. i had my multimeter on the wrong setting to get 22 V.
on the 20v DC setting, it shows 10.20 volts.
I started out testing for milliamps, I used the 10A setting first, it showed 0. then the 200mA setting, still 0, then the 20mA setting, still 0.
I tested the fueses on my multimeter, they are good.
I put it back on 20V and put it in between the - battery post and the - lead, i showed 10.20 volts. ( pdqford, i know you advised against this for damage to the multimeter reasons, but curiosity was getting me). I pulled fuses under the dash one at a time, no change. went to under the hood, there was only one that changed the reading. it was # 103 (Junction block battery feed). it dropped it down to 8.3 volts going through the negative lead.

Any thoughts are greatly appreciated about the volts reading and my inability to get a milliamp reading.
THANK YOU!

 

When you started testing for current draw, did you first change where the leads connect to your meter to read current?

I guess I'm still waiting to see if your vehicle has an excessive parasitic draw.

 

pdqford, yes i did switch it over. to the one right side where it shows the mA symbol. with a 0 reading, i switched it back over to the left where is says 10A. 0 reading there as well.
Im sure i am not using all of the correct electrical terms. my knowledge is very limited on the electrical side of things.

 

jeremyf150,
When I read that your measurements were 20 and 22V, I thought either you didn't know how to use a multimeter or your multimeter was busted. I am sure all felt the same way. I think you had better convince us neither was the case before moving ahead.

 

Paker, it was dark and i had it set on the 200 ac setting. once i put it on the 200 dc setting, it read right.
Either way, you need me to convince you i can read a multi meter and that it works before you will attempt to help?? that seems kind of backwards to me.
regardless, thank you for your time.

 

Okay. Now I know what happened. Sorry for discrediting yhour numbers.

Please describe how you meausred current draw. I hope you disconnected battery cable at - terminal and placed multimeter in between. Correct? There always is a non-zero current draw. It could be because of dead battery. At 10V the battery is dead. You cannot diagnose your car electrical with that battery.

 

I removed the negative cable from the battery, left the + hooked up, put one side of the multi meter on the battery post and the other on the negative lead. could not get a mA reading, only volts.

 

I jump started the truck and let it run for about 10 min. i am tracking how fast the battery is dying right now.
Yes you are correct, it would not turn the truck over when i tried to start it. The alternator is charging good.
Im going to charge the battery after it dies again and try my tests again.

The 0 is what had me puzzled. I have been researching the fire out of this and everything (including pdqford) says there should be a draw but under 40 - 50 milliamps. hopefully the fully charged battery will give me a reading.