I've got a 1990 7.5l f350. When I bought it the owner said it had a charging issue and that's why it got parked. Had been parked for about a month (according to him). Figured repairing the charging system shouldn't be too bad. Battery, wires, pigtails, alternator. I purchased a new battery and new alternator (2g). I installed the new alternator and got no output. Did some investigating and found the problems with the 2g and the advantages of upgrading to the 3g. Purchased a reman 3g (for a 1994 v8 mustang) Not charging. Removed wiring harness and purchased replacement pigtail and 4g wires (for the power and ground wires). Tested, not charging. Took reman alternator back to the store to be tested and they said it was good. Spent the week electrical testing. I went through all the step by step walk throughs I could find and everything appeared to test fine (I've got battery light (key on engine off), I've got 12v green/white wire, I've got good ground, I've got 12v to positive terminal on alternator). Took the alternator back the following week and wanted them to test it again. They said their tester was broken. Took to another location and they tested 2x and said it failed both times. I had done more research and found that approximately 20% of the remans (on the shelf) were failures. Decided to return the bad reman and pay the extra money for new. Installed new and tested, no output. With the vehicle off I get about 12.1 volts. When the vehicle is on and idling I get 11.7 volts. I can not for the life of me figure out what's going on. I've 10x over checked my wiring for continuity, for voltage, for amperage and I can't find a fault. All I know is I've got less voltage when the vehicle is running than when it is off. Any help would be greatly appreciated. I'm at my wit's ends. Hopefully I'm making a careless error that will be obvious to someone else.

 

Do you think that green/brown wire is the correct one? It's supposed to be lightgreen/red. Did the camera change the color or did the heat change it that much? That doesn't look right to me. If you wanted to make sure and didn't mind sacrificing your splice, you could cut the splice out, and temporarily take the green wire from the alternator and put it on the battery + and see if it charges. When you touch the green wire to the battery +, the voltage should jump up on the battery with the engine running.

 

I misspoke in the original post. The wire is green/red. The pigtail is new and the color on that is solid green. I tried just tried cutting the green/red wire before the first crimp, stripped it back, wire nutted it to a length of wire, started it up (12.1v before starting), touched the green/red wire to the battery +, and got 11.6v. I'll try any suggestions though. Thank you.

 

You can hook that wire back up if your testlight is off when the key is off, and the testlight is on with the key in run, with the testlight clipped to the ground of the battery and the probe stuck on your green/red. Or you could just keep touching that green wire to the battery + if you want to guarantee there is voltage on that wire when it's running for testing.

if you want to double check everything again;

You already checked and jumped 12v to the green wire.

I see you have the yellow wire jumped to the output lug, that should work.

Double check again that you have 12v on the large output lug with everything off. I like testlights for testing some of this stuff, it puts a load on the circuit. Your meter doesn't.

If everything above is ok, then the only other thing to do is rev the engine some while you are testing and reading the voltage on the battery. If the voltage jumps up when the rpms are raised, then you will have to check the pulley sizes and the idle rpm. If you have a decent load on the system at idle, then 12v is not abnormal, the alternator is supplying power to the load, but not charging the battery.

 

Ok, so I broke out the old test light and gave it a go. With truck off at the + lug on the alternator I've got power. I turned the truck on and tested again, still good. I tried jumping the green/red wire to the battery + terminal (while it was running) no change. With vehicle off battery reads 12.5v, on and running I'm getting 12.2v. I tried holding the rpms up (I don't have a tac, so held it to what sounded moderately high and got no change in voltage (that was with no accessories on). Turned on blower, radio, high beams and increased the rpms (for maybe 30 seconds) and got no change in voltage.

Is there possibly something in the green/red wire (someone before me) could have tied in that might be blowing alternators or voltage regulators? Or something I've done in my wiring? (The only wiring to not have been changed is the green/red). What is likelihood I purchased a remanufactured alternator and it was bad, then went back and purchased a new (new, new, NOT remanufactured) and it too is bad (these are all being purchased at the local AZ)? Still at a loss, but thank you for the testing suggestions. I appreciate your time and expertise.

 

The only thing to test on the green/red is if your testlight lights with the key on, and it goes out with the key off. And you are right, that is the only original wire you are using from the truck, everything else is new. You hot wired the green/red and still got no charging. That pretty much leaves the alternator as being bad. See if they will test it.

 

So an update to anyone. Took the new alternator back to AZ and had them test it. It tested out bad. Took it back to the AZ where I had purchased it. They treated me like there was no possible way it could be bad. They agreed to order a replacement new one and said it would be in by 1330hrs that same day. Three days later (going in everyday to get it) it still wasn't there. They then told me they had tested it and it tested good. Felt like they didn't want to bother with me anymore so they just gave me my money back (keep in mind I no longer have a core). Asked the shop where I've had work done in the past if they would get one for me and I'd pay whatever markup they felt was fair. They got me a reman (AZ had my core and my $$$ for the core, but fortunately I had a friend with a junk one sitting in his garage) Had just enough daylight to finish the hookup. Guess what 14.5v at idle. Moral of the story don't buy junk AZ (duralast) parts. Thanks for the assistance and suggestions. Happy to finally have vindication that I'm not completely incompetent or insane.

 

Sorry you had such a bad experience with AutoZone---for some reason I've never trusted them. I've always bought OEM or Motorcraft, a close second choice would be NAPA's new parts for alternators and/or starters. I have a fabulous rebuilder close by but too often I'm in a bigger rush than he can provide,

Either way for anything other than air fresheners or steering wheel covers I avoid AutoZone.