I have a 1988 F150 with a 351. A few weeks ago, my battery would lose its charge over night and the battery icon on the dash would come on when I accelerated and turn off when the engine dropped to lower rpm's. I took my truck to Advance Auto and they tested it and said it was good. A guy at work told me the brushes could be worn out but making contact at low rpm's and losing contact at higher rpm's. It was tested at idling. He also said the wires probably wore out, creating a short that drained my battery overnight. Not long after, they icon light was on all the time. I replaced the alternator and now the battery icon light doesn't come on, but the battery doesn't hold a charge while driving...it left me stranded about 1 1/2 miles from my house. The battery takes a charge from my battery charger and I had Advance Auto test it and they said it is good. I am not very knowledgable about electrical stuff, but don't want to spend a lot of money to have someone run all the tests, just yet. Does anybody have any ideas about what the problem may be or can anyone lead me in the right direction?

 

Iono still sounds like a bad battery to me...or a hairy voltage reg.....check all your wires from your battery to your solenoid and to your starter and frame.....especially the grounds.......Your battery might have a low water level as well.......

JR

 

You are going to have to do some trouble shooting.
As I see it, you have 3 possibilities.
1. Alternator not charging battery.
2. Battery is bad and not holding charge.
3. Something draining the charge from the good battery.

Here is how I would approach the problem.
For #1, use a mulitester. A real cheap one will do the job. Measure the voltage between the battery terminals with the engine off. Should be around 12.5
Then start the engine and measure the same way with the engine running. Should be around 13.5-14volts DC.
If it is not coming up close to 14 when running, the alternator or the internal voltage regulator or a connection in the wiring is bad.

For #2. Charge the battery up and disconnect the negative battery cable, and leave it over night, Reconnect the cable and see if the battery starts the engine. If this is ok, then your battery is probably ok.

For #3 you need a test light. Pretty cheap and handy to have. Got mine at Harbor freight for $4. Disconnect the negative cable again, and hook the test light between the battery post and the disconnected cable end. Do not turn on any high draw electrics, like headlights, or try to start the truck. You should see a dim glow to the test light. This is from things like the radio and the computer drawing a tiny amount of power to keep the memory alive. If the light is glowing brightly, you probably have a short somewhere that is draining the battery.
When you disconnect the battery for a few minutes, the computer looses its memory. It will have to be driven for a few miles before it runs correctly again. It will still start and run, it just may not idle smooth and idle too fast or slow, or run a little rough. Don't panic, it will solve the problem in a few miles.
After saying all that, I would just guess you probably have a bad battery, but I would test the alternator output before I did anything else.
Good luck Frank

 

Fmr9 had lots of good info there.

The only thing I would add is was the battery ever load tested? Advance Auto and other places will do that for you, unfortunately lots of times you have to ask, "usually" their batttery check is what fmr9 described which shows the battery is putting on the correct 12 voltage, but the battery can be putting out the correct 12 volts and not be able to start or run the car due to bad cells or wavvy plates etc. etc.


Good luck!

Paul

 

He may have a blown fusible link, I had an 87 Cougar and I blew my fusible link and wouldn't let the battery hold a charge. Just a suggestion, may not be the right one. Get a test light and check'em out.

 

Thanks for all of your suggestions, guys. I think I have it fixed. I believe there was a short in a wire inside the connector to the alternator. It was the wire with the fuseable link. It appears to be charging the battery now.

 

Glad to hear it...keep posting golfdude and don't be a stranger....

JR

 

I am having the same problem, and I have performed all of the tests but the "test light". I was wondering, how much voltage should be drawn from the negative battery cable and the battery post? I show 12.5 volts. Is this draw, or are amps different?

 

There is always some tiny draw, things like computer and radio memory need 12 volts but use milliamps of current.
You will always see 12.5V (or so) at the battery.

Voltage is potential
Amperage is current
Watts are draw, work, or "what is used up"

You could have all the voltage in the world, if there's no current flowing, there's no work being done, and no drain...

Ohm's law shows Amps x Volts = Watts

Electrical & Electronics, Ohm's Law, Formulas & Equations

Try removing fuses one at a time and see if the draw stops.
Try unplugging your alternator, and see if the battery goes flat overnight.
As was posted above the wiring harness plug is a weak spot that fails often enough that replacement plugs are common in the aftermarket.

Hope this helps.

 

I switched my multi-meter to Amps (20/10A) and I am pulling only 0.38. Is this a problem? I have the battery disconnected to see if the battery loses amps.

 

1/3 of an Amp?? sounds like a bulb is on....(just under 5W)

I STRONGLY recommend if you must use a meter, use a clamp-on type for this, rather than risk putting your meter inline with the cables.
This is why a test light is recommended. The filament acts as a resistor, if there's enough draw to brightly light it up you have an issue, but it will only flow so much current. (of course make sure the door is closed so the dome light is off)

It is voltage that is stored in the battery.(so to speak) That is why you measure state of charge in voltage.
You'll need a battery load tester to see if your battery is shot.
Almost any Service Station or Auto parts store will be glad to do this.

Have you tried pulling fuses one at a time?
Have you tried unplugging the alternator?
If neither of these work then I would start looking for a shorted plug or
chafed wires.

How long has this been a problem?

 

Hello:

Check for burned wiring as well that is attached to the alternator. Two weeks ago, I was replacing my alternator. After having unhooked it, I reconnected the battery to the truck so I could move it. A minute later smoke was in the engine compartment.

What happened was, I left the negative terminal from the alternator dangling, and it shorted to the metal of the engine. It smoked especially near the battery. I thought there would be an explosion.

A week later, after having replaced the alternator, the battery wouldn't charge. I found the burned wiring at the fender going into the starter solenoid. After reattaching it, it charged.

This is just my recent experience, but do check for that or maybe you can help someone with that advice.

Steve