Hey guys,

My batteries are not keep a charge for more than two days and I'm thinking there might be a short. The batteries were replaced last year so I don't think they've gone bad. I'm pretty sure the alternator is functioning correctly (charging my batteries) because the truck will start fine if I drive it everyday.

I'm just looking for a little electrical advice. I have a multimeter and I know how to test for voltage and continuity. My question is where should I start testing. Has a write up been done on basic circuit testing for our trucks? Some simple advice in the right direction would be a great start. Thanks guys!

 

The simplest would be to check Pos and Neg cables at both ends. Next easiest would be to check the positive wire on the alternator. Someone else will chime in

 

CHIME!!!!

(Somebody call?)

The very best place to dig into this is in the electrical forum here - there are people there who can run circles around any other electric system troubleshooters on the planet in that forum.

If you have a dual battery system, disconnect the negatives from both of them.

Then connect an analog (NOT digital) meter between the neg post of one battery to the negative lead. A TEST LIGHT works even better. If it reads a solid twelve volts, or if the test light lights up brightly - you've got a full 12V drain from somewhere.

Next thing to try is to leave the test light connected and begin pulling fuses until the light goes out. Replace the OTHER fuses and hope it doesn't light back up.

The circuit that is left is the problem.

If ALL the fuse are pulled, and you still have a bright light - undo the alternator charge wire at the alternator. If it goes out then, likely the ALT has a bad diode pack.

THIS IS THE FAST CHECK! If it doesn't turn up something definite - you need the FTE electrical crew!

The reason for a test light is because there are low ampere "KEEP ALIVE" things like your radio memory that only pull a very small amount of current (microamps). A DIGITAL meter will call it a full twelve volts, but a test light won't even glimmer. A dead short is a different story...


~Wolfie

PS: AGAIN - the electrical forum has the top dogs at finding these kinds of problems.

PS: With all due respect to Megawatt - a shorted battery will do that. Heck, I agree absolutely! But more often either a drain, or a failure to charge is the cause. And that can kill a set of battery plates (dead short a cell).

Believe it or not - dirty positive connections can cause more batteries NOT TO CHARGE than any other culprit I can think of...

We ALL pull the negatives right?

PULL OFF THE POSITIVE AND LOOK AT IT FOR ONCE!

 

There are a few simple test that you can do to see where your problem may lie. 1: Start your truck and check the voltage output of the alternator. You should have around the 14V mark. Put your headlights on and do the same test. The voltage may drop a little but not much. (The voltage reg. should kick up a notch to compensate.) 2: Check all connections including grounds make sure that they are clean and tight. Also check the wiring to the alternator to see if there is any chaffeing. 3: If these 2 don't work .disconnect the batteries and do a load test on each battery seperately. If you have even 1 bad cell it will pull the rest of the "bank" down.If all these check out ok then post back and we'll help you find the problem.

I had this same problem with my tractor 6 mo old battery and it crapped out. Jump it it would run all day. Sit for a day and I'd have to jump it again.

 

BATTERY SIMPLE TEST

1) Charge it

2) Let it sit.

3) Test it.

If it died, the summitch is shorted inside.



OOPS.... Oh well...

The smartest thing I ever heard a tech say was a question:
"HOW CAN I PROVE THIS THING IS EITHER GOOD OR BAD?"

 

Thanks for the input guys. I only have a digital meter right now so I'll go pick up a light tester and some scrubby pads for my battery terminals. It's over 90 degrees out right now so I'll wait until this evening and report back.

CHEERS!

 

Hey guys,

Still need help with my situation. I've been in mexico for about a month, good times. Guess what though... batteries were completely dead when I got home.

Took my probably original (motorcraft batteries) and sure enough, dead. Bought two new ones 850cca.

The truck starts really quick now but I'm pretty sure I have a dead short. I disconnected my driver side battery to confirm that I did get a 12volt light between the post and neg. terminal.

I also took my truck in yesterday and they ran a test on the batteries. The driver side is reading 12.76, while my passenger side was reading 12.57 volts. Is this normal? I was thinking that the short might be on the passenger side.

What should I do next guys? I really appreciate the help!!!

 

I'm gonna redo everything greywolf said to do, I'll post again tonight. Thanks!

 

If you are stuck with just a digitial meter, you can change over to the amp setting, This will tell you if it is a real load, or .25 amp just another thought!! Good Luck

 

A diesel has a dual battery setup, so it gets interesting seperating out faults.

The positive cable usually goes straight across the front of the truck with a terminal for each battery positive on it. When doing the negative post stray voltage test I suggest undoing the positive post on the opposite battery to check one at a time.

If both battery connections are good, and have no big volt drains - the next big question is do they charge well?

Since both batteries are new - they should be okay. If there's doubt - charge them both (the alternator should raise the voltage to thirteen or more volts on each + post. BOTH posts should read the same.) and unhook the negatives on both overnight. Test the voltage on each disconnected battery before closing the hood.

In the morning (before connecting them) read each battery for voltage from post to post. THAT tests them seperately. If one fails to hold a charge, overnight should show it.

While the negative clamps are off there is one more thing to look at - is the path from EACH negative cable clamp TO GROUND on the ALTERNATOR (seperately, as in one at a time) less than one ohm? YES - I actually go from the negative clamp to the alternator housing by preference. I have found badly grounded alternators before...

 

Quick looking for a dead short and don't have the correct meters find a clean spot on the bumper and touch it with your tongue.

 

I found that only works for bikini's - but it's more or less guaranteed to fetch a knee in the shorts...

That would kill your shorts for a while tho.

 

Sound dumb - but it happened to me.

Make sure the light in the glove box and under the hood are going out.

They WILL kill a battery.

Then go on with the procedures listed to check charging systems, etc