Hey guys,its me again. You all were so helpful with my FI problems,I thought Id try this. Heres the details..96 F-150 4.9 I6 2wd auto.
The problem started a few weeks ago. I started truck fine,went to the bank and it would not start. After useing Jumper Cables for 10-15 min no start. I tapped the starter with a hammer and it started right up. Ok I get the starter rebuilt,starts fine. A few days later...wont start after sitting a couple days. I hook up the Battery charger and its half dead. Ok so I get battery tested and he says its weak. $79.95 +core I got a fresh Northstate Battery. I go back to swap out core,I was gonna use the old battery in my 5.0 Mustang that has an even older battery.

Today I compare the two batterys to see whos stronger. Neither have been charged in 3 or 4 days. The one I pulled from the Truck has a full charge!? It would be dead if it was in the truck. So for curiosity I hook the charger to my NEW battery in the truck and its down 1/3 after 3 or 4 days of sitting!? WTH? I know the ALT is charging because I unhooked the battery while the truck was running and it kept running. This is a new less than 1.5 year old High Output Alt. I still have the old one as it was good. I know I need to check the Alt for proper charging BUT what could drain a new battery so Quick? Sorry for the long read.
Any help or suggestions would be great. Thanks in advance...T

 

If the alternator has a blown diode it can charge while turning and still drain the battery when it's not turning, even with the key out.

If you have an electrical tester you can remove one battery cable from its terminal and connect it in between.
Go to the solenoid and remove the nut holding the + cable there.
Remove the other wires (fusible links) on that post and touch them one at a time to the positive cable.
You will find which one is the draw.

 

also, removing the cables from the battery with the engine running will put the alternator in full output mode and usually burns something out.

it really sounds like you have a bad diode letting the battery drain like Jim said.

 

Ok guys, lets dumb it down a little.

What solenoid ? Where? On the Alt or on the inner fender?

I only unhooked the battery for a couple of seconds to test then Quickly re installed. Thanks for the help...T

 

The thing on the fender that the positive battery cable connects to is the solenoid we are speaking of.
Your late model truck may have a PMGR starter with a solenoid on it too.

The act of disconnecting the cable while the engine is running causes a voltage spike when the alternator is "told" that there is zero voltage.
That "reaction" by the alternator is often enough to damage it.

It is also NOT a good idea to just let an alternator try and charge a really dead battery.
For much the same reason.
If your battery is 10V or so, it shouldn't be a problem.

 

Ok I just looked on the fender and saw the solenoid. If and when I find the problem,how do you go about fixing a bad diode? Where do these fuseable links run? Where would the doide be and what does it look like? Is this a simple fix? Cheap? Im still unemployed and the battery and starter already hurt. I can reinstall the stock Alt if I need to. Can it be tested while on the truck? Really Thank You again...Travis

 

The rectifier inside the alternator is made up of diodes.
These act as a one way valve for the electricity your alternator produces.




You can test for current drain as I described above, but often you can just come out in the morning when it's dead and -feel- the back of the alternator for warmth.

 

Travis,
We don't know what's bad without doing some testing.
There are no clues for us (like melted wire insulation, or a faint aroma of burnt windings) over the internet.
We don't even know if it is your alternator that is at fault yet.

The fusible links individually connect different wiring systems in your truck to the battery.
You might have one going to your ignition switch and another for things that are always powered and yet another going to your alternator.

You say you have a "High output" alternator.
What does that mean? 130A, 160, 200?
These will all have different regulators, and of course you can buy anything from no name Chinamart crap to OEM to replace them.
The 130A rectifer I pictured is $40.

Hope this helps.

 

Quick check, with the engine not having been run for a while, see if the alternator is hot, or at least warmer than the engine. If it is then you have one or more shorted diodes. Your high output is probably a 130amp unit. The fusible link is at the end of the alternator harness where it attaches to the solenoid.

 

Ok I just went and felt up my alt. It has not been ran in a while and its cold out. I didnt feel any warm spots,although the plastic is not as cold as the steel. Ill try it again tommorow.
I THINK its a 160 amp as I bought it as an upgrade to stock,I was driving short trips at the time to work and such. I thought it would help keep the battery charged better. Its a Palladium brand from Advance Auto. The box says assembled in USA...Who knows what kind of parts.

Im kinda stumped I may just reinstall the stock Alt and see if this helps,after I try the other suggestions first. My key switch is broke,has been since I owned the truck. It still functions but I can remove the key while running and start without it. Lately it dont click firmly in the off position. I guess it may cause a drain. I was leaving my GPS charging all the time but I unpluged it when this problem started.
Thanks again for all the help. Ill LYK what happens...T

 

Even if you don't have an electrical tester you can get a probe with a lightbulb and a clip-on wire for a couple of bucks.
The test I outlined above will start the troubleshooting process.

 

Update...I swapped out the Alt, Battery still drains overnite. So I go to the starter shop. Alt is charging at nearly 14 volts. When I cut the motor off..You got a short pulling 13 volts. Oh goody!
I hook-up my cheap test meter and pull fuses from the box one at a time,no change. Ok I put the meter between the battery + post and POS cable un-hooked. I remove the wires on the out side of the solenoid and touch them one at a time back to it. BOTH wires cause a Big drain,one a little more than the other.

I had asked the guy if he thought it was a solenoid problem,he said they very rarely cause a problem. Im thinking that IS the problem. Any thoughts or suggestions...? Im headed to the parts store in the mourning for a new one.
The old Alt checked out too. Thanks again...T

 

You need to measure AMPS draw.
A voltage reading at the positive terminal is telling you nothing.
Voltage is analogous to pressure and even the radio memory will draw 12V, albeit in milliamps.

Like I told you, you can still have an alternator that charges when turning and draws when stopped.
WHAT wires did you disconnect? (I have 5 on the 'Hot" terminal of my solenoid)

The solenoid rarely shorts to ground.

THIS is why I suggested disconnecting everything from the hot terminal and touching the wires individually.
By doing so you have eliminated the solenoid as the cause.
OR, maybe your ignition switch not clicking to the off position is leaving some unfused circuit on.

Either get yourself an incandescent test light or use the amps setting of your meter, if it goes high enough.

 

I removed ALL the wires except the one coming from the battery itself. It has a wierd little plate/bracket that touches to both sides. I forgot to say I had replaced the Key Switch. Im thinking this would be a easy try at fixing the problem. I can return the solenoid if I dont need it. I cant find my test light...T

 

What setting is for AMPS? I was on DC V 50 setting. DCmA or ACV ? All these settings look like Algebra to me. Thanks...T