No output from alternator

[ahardb0dy]

I'm posting this here because this may also apply to the R50's with the VG33.

 

My neighbor has a 2000 Xterra, VG33, he says the alternator is not putting anything out when checking it using a multimeter at the stud on the back of the alt. He has had the auto parts store test it three times and each time they say it passed, he even has had them replace it once.

 

No fuses are blown or missing under the hood or in the truck.

 

The truck was set up by the previous owner with 2 batteries in the rear cargo area with an isolator and a kill switch, he is using only one battery at this time.

 

Any idea's on what to check or what may be wrong?

 

Thanks all !

[Precise1]

What voltage is at the battery terminals when it is sitting with the ignition off, sitting with the ignition on and then when it is running?

 

B

[ahardb0dy]

Not sure at the battery, haven't looked at it yet, He had asked me about the large fuses in the fuse block under the hood, 2 -80's and 1 - 100 amp, the 80's come right out but the 100 amp seems to be stuck, possibly it's bad I don't know. He didn't want to force the 100 amp fuse to come out without having one to replace it in case it breaks, the 2 -80's have what looks like corrosion on the top of them but I checked them for continuity with my multimeter and they both tested good.

 

At the fuse for the alternator in the same fuse block, 7.5 amp I was getting normal battery voltage mid 12 volts.

 

Looked at the wiring diagram and is shows the 7.5 amp and the 100 amp fuse are for the alternator, so the 100 amp could be the problem. Will talk to him later when he gets back home. Also do not know if the charge light is on.

 

Thanks

 

 

[ahardb0dy]

So My neighbor checked al the fuses I told him too and they were all good, he says the alt test good on the auto parts store's machine but still no output when in the truck, I'm thinking there is a problem with the wire that tells the internal regulator to turn the alternator on, going to look up the wiring schematic, I told him a little while ago if I can figure out what wire it is we ( or he) can run a wire from the alt plug directly to the battery and that should tell the alt to turn on, if it does and starts putting out voltage than I guess there is a problem some where between the alt plug and where ever that one wire is reading battery voltage.

 

Sound right?

 

Thanks

[ahardb0dy]

Is the stud marked in red in the pic below ( inside the fuse box under the hood, 2000 Xterra ) a positive or a ground?

 

 

[ahardb0dy]

Well my neighbor solved his charging problem he no longer needs to plug the truck in every night !

 

He finally did what I suggested and eliminated the battery isolator, and the battery started getting 14.5 volts.