ive got a pretty bad problem here, my battery wont charge for some reason. i have an 86 F-250 4x4 with the 4.9L(300) I6. ive replaced the alternator and the voltage regulator and it still wont charge. im pretty sure its not the battery because ive charged it with my "household" battery charger and it holds a charge no problem and registers as 12 volts on my digital multimeter. the strange thing is, if i remove the cables from the battery it works great and i get full power at around 14-15 volts(wich would indicate that its chargeing). if i test it while its connected to the battery i get around 11 volts and everything is dim and sluggish. eventualy the battery will die if i leave it like this and i wont be able to start it again. why wont my alternator charge when hooked up to the battery???

 

Clean all connections on all major wires. Check for corrosion under the vinyl insulation on the major cables...if present, replace.
You could do a continuity test on each wire, but you still need to clean where it connects.

 

ive replaced both battery cables and connectors and the wire going from the alternator to the positive terminal on that little solenoid. ive also tested the output comeing directly off the alternator and it drops down to 11 when i connect the cables to the battery. ive tryed moveing the wires around to see if the voltage would increase but it doesnt. as much as id like to try replaceing the battery, i dont know if im willing to drop 100 dollars on a guess. does anyone know what exactly this voltage regulator does to the alternator to make it kick in? ive tryed wireing the "field" stud directly to the positive terminal to see if it would at least charge it enough to get me home when it first broke down and it looked like it was working for a bit, but stopped.

 

find another battery to try, even if it's just a friend's, for a test to see if it still draws down while running.

 

I have the same problem. Did you find the problem? I could use the answer? I havew replaced the alternator, regulator and battery. I still goes dead and the output from the alternator is very low........but its all brand new?

 

well, since then ive dropped a 351W into my truck. wich by the way id just like to state does not bolt up to the cross member despite what everyone has been saying, i had to fabricate an entirely new mount system for it because the mounts sit about half a foot behind the crossmember. i did however come across some interesting wireing problems. over half the ignition activated power sources were produceing alot less than 12 volts with or without the alternator working, wich im guessing could have seriously affected the voltage regulator. if your haveing this problem too, i highly suggest buying a digital volt meter or a circuit tester that displays the voltage reading.

 

Ok-thats my problem. Now, what causes that and exactly how do you fix it.
I read the low voltage on the digital mulit-meter-but what is causing the problem AND how do I fix it. I don't know the cause, where it begins or how to correct it.

Why would the ignition ( switch?) affect the voltage regulator?

 

almost everything in vehicals runs off 12 volts, if the voltage regulator isnt getting a 12 volt power source it might not be activateing the alternator. im not 100% sure how the voltage regulators work, but i know that replaceing both it and my alternator didnt fix my problem, so all i can think of is it must be a wireing problem somewhere. wireing problems are hard to track down, it could be a worn out relay or it could be corrosion or a break in the wires somewhere. as far as i know theres 2 kinds of alternators, internaly regulated ones and externaly regulated. if yours is externaly regulated you should see a little grey or black box on the passanger side fender wall with a bunch of wires going into it. if i were you, id just go buy an internaly regulated one off a newer truck or a performance parts store. ive heard you can get one off a 90's ford taurus with the same bracket style and it will bolt right on. theres also kits out there that can turn your externaly regulated alternator into a 1 wire self regulateing alternator.

 

Psyte, it sound like you have a short that is drawing down the battery!

When you reconnect the battery cables do you get a little spark?

Here is a test: Disconnect the neg battery cable. Connect your volt meter between the cable and the battery. With all systems turned off, including the interior lights, glove box light, underhood light etc. there should be no reading if all is well. If you get a 12v (or so,) reading, you have a short.

If you discover by the test that you have a short, then pull fuses one at a time until the reading goes to zero. That will identify the circuit that is shorted. If not, disconnect the alternator and see if it goes to zero then.

Post back to let us know how it goes.

 

As for the "ignition" activated parts seeing less than 12 volts even with the alt working, sounds like you have bad wiring in the ignition system or switch. The ignition system of most older [carbed] ford vehicles runs at only 10-11 volts. There's an inline resistors that drop the voltage to the ignition system from the standard 14.5 "running" volts to just 10 or so while the key is in the "run" position. If the ignition switch is faulty [or one of it's connected wires] your switch dependent accessories could be getting "back fed" through the resistor. This is one of those "shouldn't ever happen" kinda' things, but I've seen it occur.

 

i did that test that you mentioned and it reads around 12 volts when i test from the negitive terminal on the battery to the negetive cable. it dropped to around 11 volts when i removed the "courtsey" lights fuse and it was the only fuse that made any kind of a change with the ignition off and on. also i noticed im not getting much of a spark when i connect the battery cables, and that when a positive wire touches the frame i dont get much of a spark either compared to my car wich almost gives off fireworks when i touch a positive wire to the frame. what should i do??

 

OK. - I fixed mine and all works perfectly. Here was the problem. I had no charging at all from the alternator and replaced the voltage regulator, alternator, battery, starter solenoid and re-did all the wires to the ignition switch and even replaced the ignition switch, then after all that I had too much charging (18.75v) to the battery and (49A). I happened to be a the local auto parts store looking through Chiltons and realized that the voltage regulator MUST be grounded. My engine compartment was repainted black and the voltage regulator was not getting a good ground. I got another regulator( blew up the other one ) installed it with 2 really good ground wires goint to both mounting holes and ran the "I" wire to the ignition mount on the ignition switch back. Started the truck and its perfect. Charging at (14.75v) and (39Amps) from the alternator to the battery. Note** DO NOT pull the battery cable while the truck is running to see if you are charging-when you do this you will blow the voltage regulator-I went through 4 voltage regulators through trial and error. Good thing the Auto Zone gived a 90 day warranty. If you need a wiring diagram, send an e-mail to
>Hiball3985@aol.com< and tell him Steve sent you. He drew one for me and it was perfect. Tell him I sent you. He knows his stuff. Good luck!

 

With all systems off, you should get no spark when you attach your battery cables. That idicates that there is a current draw, (same as the voltmeter test.)

Did you disconnect the alternator when you were doing the current draw test?

Again, as a test, connect a jumper cable from the battery neg to the engine and see if it charges. (to see if the engine to chassis ground is not working.)

You need good grounds everywhere, if they are not working you can get all kinds of peculiar symptoms. Battery to chassis ground, chassis to engine, engine to firewall, chassis to radiator support.

 

"Kinda along this same line", I found a bad wire coming from the alternator. '89 I-6 4.9 FI 4wd HiBoy was not charging at all. Changed the alternator and battery at the same time just to have them new (had just bought the truck). No improvement. Been a long summer and have not had the chance until tonight to look at it again. Tonight I found that a *monster* (maybe #6/8?) wire coming from the Alternator had what looked like a fuseable link inline. When I twisted it around, the alternator kicked in. Let it go, then after a few seconds the alternator kicked back out. I sliced the thick plastic sleeve on the monster wire, and instead of a fueseble link found a really $#1tty wire repair that was covered by a shrink-tube larger than any I've seen. Have no idea why the wire was cut (very clean cut) in the first place, but tomorrow I'll go get a monster in-line fuse holder if there is one large enough to carry the alternator output, or else just get a package of #6/8 connectors. Can't find anything in any of my manuals that shows that monster wire, so don't know if it had a fuseable link in a prior life or not. Several starts to move the truck around had run the battery down quite a bit so am charging it tonight so it will be full tomorrow when I see if the charging system is finally operating properly. At least, after I fix the wire I'll check the charging rate at the battery (supposed to be more than .5v but not over 2.5v). So anyway, that's my 2c worth for tonight, for what it's worth. ;-)

 

Just thought I'd add... Sometimes a digital volt-meter is fantastic, but my personal preference for testing for a current draw (short) is to connect a test light (between the battery post and the terminal). Just my preference.