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Discussion Starter · #1 ·
I just swaped out my alternator for a 130amp i pulled from a junk yard. i took the alternator and got it tested and it worked. i put it on my truck yesterday and i moved it like 40 ft. it ran for about 2 minutes total. today, i went to move my truck back and it wouldnt start at all. i jumped it off and it started up but idled sporatically and when i took the jumper cables off, i could watch the battery meter on the dash slowly drop down untill the truck cut off. what do yo think the problem is?? it ran yesterday, but not today. do you think that the battery is going?? like i said, when i jumped it with the superduty, it ran fine, but as soon as the cables were removed, the bronco slowly lost power and turned off. i originally thought that it was the alternator but i had it tested and everything was fine. any ideas what i should check for?
 

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Make sure that you have all the necessary wires connected to the new alt. There's a yellow wire that needs +12V on it for the alternator to work. It was buried inside a wiring harness on mine.

What's the voltage across the battery when it's running? If it's not +14V or so, the alternator isn't producing any power.
 

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Discussion Starter · #8 ·
the voltage is not 14 volts. it goes down from 14 to 12 to 10 to 8 to off and this decrease starts as soon as i take the jumper cables off. is the little yellow wire you are talking about connected seperate than the three wires in the one plug?? i will triple check the wiring again but im pretty sure i have it right.
 

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Your alternator isn't generating any energy, then, as you have it installed. I'll bet it's that yellow wire. Did you change out the charge cable as well, or just the alternator? The wire I'm talking about connects to the same post as the charge cable. Check out the wiring diagrams on fordfuelinjection.com.

I'll take a picture of mine tonight, if I can. I remember I scratched my head over this for hours the night I installed my 3G.

edit: read the last post here

http://www.fullsizebronco.com/forum/showthread.php?t=64870
 

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Sounds like the battery doesn't have enough power to "excite" the altenator. The battery has to have a certain amount of power in order for the altenator to work. Try charging the battery.
Also check to see if there is a drain on the battery when everything is turned off. I did have an altenator that drained my battery occasionally.
 

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Discussion Starter · #11 ·
slaga said:
Sounds like the battery doesn't have enough power to "excite" the altenator. The battery has to have a certain amount of power in order for the altenator to work. Try charging the battery.
Also check to see if there is a drain on the battery when everything is turned off. I did have an altenator that drained my battery occasionally.
how did you stop the alternator from draining the battery??
 

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96broncoman said:
how did you stop the alternator from draining the battery??
Replaced it, but I made sure it was the culprit before I replaced it. The altenator wouldn't drain all of the time. It had to stop in a certain position in order to drain the battery.
 

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Discussion Starter · #13 ·
hmmm, well when i put the alternator in a week ago, the truck started right up. then, the following day, it had to be jumped off although the lights and radio still worked. today, nothing works, no radio, no lights wont start. think its the alt??
 

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Your voltage readings are showing that the alternator isn't producing any power. If you run the truck like that, it's running off the battery only, which isn't getting recharged at all. Make sure your wiring is good, charge the battery, get that alternator working, then see what's happening over time.
 

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Discussion Starter · #15 ·
sewiv said:
get that alternator working
not quite sure how to fix it. lik take it apart? what should i look to fix? pretty much clueless. should i start pricing a new one?? i dont drive the truck much but i could put the old alt in to see if it will work for me...but i will have to switch out to the higher output with my electric fan. but could i use the old alt to diagnose the problem?
 

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Put the old one in, see what it does, see what your voltages are at the battery. Did you change anything other than the alternator itself? Change any wiring? Upgrade the charging cable? Anything?
 

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Discussion Starter · #17 ·
sewiv said:
Put the old one in, see what it does, see what your voltages are at the battery. Did you change anything other than the alternator itself? Change any wiring? Upgrade the charging cable? Anything?
nope, just changed the alternator. do you think that may be the cause, not upgrading the wiring. i pulled the new(currently not working) alt. from an exploder so i figured that the wiring on the bronco had to be handle at least the same amps, it not more. i guess i may have been wrong. if i get one of the alt. wires from fordfuelinjection.com, will that replace everything i need to upgrade??
 

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No, the only reason to upgrade the wiring is to handle the higher amp flow to the battery from the alternator, keep the charging wire from burning up. If you didn't change anything, you should be able to plug in the new alternator and have it work. Try the old one, see what you get. If that still works, then your wiring should make the new one work. Don't worry about the charging wire upgrade until you have a working high-amp alternator in there.
 

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Discussion Starter · #19 ·
ok, i put the old alternator(the one that was working perfectly before i wanted to upgrade) back in and had to jump the truck off. when ever i removed the cables, the truck cut completely off very abruptly. even after keeping the cables on for a long time the truck just cut off as soon as they were removed. also, the dome light which had a lil power this morning wont come on at all now. so is the problem the battery?? would my high-amp alternator work if i had a new battery?? how can i make sure that the alternator isnt going to drain a new battery??
 
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