I bought a 2001 Ford Excursion v10 4x4 with 143k miles unseen except pics from a northern dealer. He painted a one owner truck with light rust and just a great vehicle. Some lessons you learn the hard way. Anyways the first night I get home and start it and the battery is dead and won't start. For some reason this also set the theft system off. I couldn't try to start it without it going off. I unhooked the negative on the battery and let it set and then jumped it off. My kids had actually got in it to check out the new vehicle before I got home and left a couple lights on. That may be what killed it or may not. The lights even though left on had already went off. Once I jump it off to my surprise the battery light is on so I grab my meter and its not charging. My battery charger had went out last week so I get another one the next day and charge the battery to rule it out, I charge it up good, start it up and still the same condition. I assume alternator is bad and remove it to get another one. I take it to O-reillys and they test it to check before I buy the new one and say everything shows good but could be the battery. I go back home put it back on and drive it to O-reillys. The charged battery held voltage good enough to stay around 12v so i was able to actually drive it, plus I had to actually drive it to the DMV to get the vin checked before I could get my tag. They check the battery and its good. I decide their machine is probably wrong and pull the alternator. They check it 4 times and all show good. The machine even showed how much voltage it was putting out. I still tell them I wan to try a new alternator. Their policy is normally once you put it on you can't return it but they say they'll just let me try it anyways ( very pleased with them on that). I go back out and put the new one on and same thing, no charge. At this point I'm not really sure what to check. I'm not the best with electrical but with a little help I can probably figure it out. Assuming my battery and alternator are actually good is there any fuse or anything that I can check, or where do i go from here? Thanks in advance

 

 

Messed with it a little more and have a quick question. Where does the alternator itself get its ground? When I touch my positive cable to the main wire come from the alternator I can touch the battery negative and it shows the battery voltage of 12.4v. When I touch the negative to the housing of the alternator I get less than 1v. I tried touching the little bracket on top of the alternator and the bottom screw that actually bolts the bracket to the alternator shows less than 1v, but if I touch the top bolt it shows the 12.4v. Is this normal or do I have a ground issue?

Update. I cleaned a few ground wires close to the battery box and now I can get voltage when touching the housing of the alternator, still not charging though.

 

Check on the alternator, you should have a lightgreen/red wire going there. Take your meter and put the negative lead on ground, and then with the key off you should have nothing on the lightgreen/red, with the key in run you should have around 12v. If you don't, that is a problem. You can put a jumper wire on that wire and see if it will charge. You can't leave the jumper on it, the battery will run down. This wire brings the alternator "online" to charge when the key is in run and comes from the cluster light in the dash.

 

I done what you said and I'm getting right close to 12v with the key on. Where next, is there a simple fuse or relay I could be missing?
Update I found a fuse control panel diagram on line and the fuse was good. If I removed the fuse the battery light on the cluster wouldn't come on. Can I test for voltage actually coming out of the alternator? Is it possible I'm losing it between the alternator an battery?

 

With the engine off, if you have 12v on the output terminal of the alternator, we can assume that is coming from the battery and it is good. You were checking that when you were repairing the ground correct?

Do you have a jumper wire on the alternator also? It should be the white/black in the diagram below. Even though the diagram below is a older alternator, yours is still wire mostly the same. The yellow/white wire is the voltage sensing wire for the internal regulator.

 

Here is my alternator

The yellow wire at the back goes to the battery. With the truck off or on I get whatever voltage the battery has when testing it. The plug with 3 wires has the light green/red you mentioned and it has 12v with the key on. I assume the single wire that connects in with the 3 plug senses the voltage.

 

The single wire is the jumper I was talking about, it is for the stator of the alternator.

You seem to have everything there. 12v on the large output wire, 12v on the yellow/white sensing wire, 12v with the key-on for the green/red.

I would double check that ground again. I have seen trucks from up north that were unusually rusty have problems with that. They are supposed to ground through the brackets but corrosion can cause problems. I had one that was so bad I could not get the bolts loose, so I just ran another wire from the case of the alternator to the ground on the battery negative. With the truck running, take your + meter lead and put it on the battery +, and then take your negative lead and put it on the neg of the battery. Make note of the voltage. Then move the negative to the case of the alternator and see what the voltage is there, with the + lead on the battery + and the neg lead of the meter on the case of the alternator.

If the ground still checks good, I would take the alternator back and get it checked again. I know you think I am crazy, but I bet they won't say anything. It's not unusual to get a rebuilt alternator from the store that does not work. It might have been the case of your old alternator was good, you swapped it out with a bad one from the store, you stumbled onto the real problem and fixed it(the grounding) and now it still won't work because of the faulty alternator they gave you. That is one scenario I can come up with.

 

As far as the alternator goes I actually have the original still. They were nice enough to let me test a new one on the vehicle without buying it. I still have the original one on right now. The ground is not real consistent when doing like you said. There are places I touch the housing and the voltage is good and there are places with nothing. The bracket has 2 bolts that hold it on, one bolt has good voltage the other no good. The single wire in the pic that is either yellow black or white black I am getting no voltage on it key on or off. I'm just putting my positive lead on it and negative on the battery. Maybe this is my problem? Can I run a jumper from the battery straight to that terminal or will it hurt anything?

 

Another update. I decide to replace my connector because I read where they needed replaced if you messed with the alternator. I replaced the plug and put another ground from alternator to the battery, still nothing. When looking at my picture the big red wire has 12v and the green/red when the key is turned on. The center yellow wire that goes from the 3 wire connector to the single connector has nothing. I'm assuming this is my problem. Franklin if I don't have 12v there what is the cause? Thanks

 

That single wire only has voltage when the alternator is turning. And even then it's only around 7-8v usually.

 

I'm only getting roughly .007v on the single wire that comes in from the 3 plug while its running. This thing is driving me crazy. Could both my alternator and the one they gave me to test be bad? The odds seem awful slim but at this point I don't know. There is an older man that rebuilds them in town. Would I be better off getting the original rebuilt vs a re-man ? I appreciate all your help.

 

 

Is that a typo above? You should have 12v at all times, engine off, key off, or engine running on the yellow sensing wire. You should not have 12v on the green/red wire with the key off. Key on engine off, yes, key on engine running, yes.

 

The green red wire is 12v only when key is on. The outside red wire is 12v when off . The center wire which goes also tpo the single wire does not have voltage any time I have checked it.


Sorry that was a typo. I went back and fixed it. The green/red wire only has 12v when key is on not off