Possible Alternator Shorting Out Electrical???

[TBigLug]

I've got an electrical problem on a carbureted 350 motor. When the plug is in the back of the alternator it draws my battery down to nothing. Draining all the juice as if I left the headlights on. If I unplug it the drain goes away. When the truck is running the alternator works properly as if nothing was wrong. I tested the plug with the key off and get 12.6 volts at each of the wires in the plug. Is it possible something inside the alternator is shorting out and draining my battery or is the problem downstream somewhere? I looked at my wiring diagrams (if you want to call Haynes versions that) and according to them one wire goes to the ignition switch and the other to the gauge on the dash. To add to the confusion, this motor was put in sometime between 1994 and 2004 ish as far as I can tell. Should either of these wires even have juice to them if the plug is out? I went through the fuse box one fuse at a time pulling them all out and it didn't effect the drain at all. So it looks to ma as though the drain is somewhere between the battery and the fusebox. No melted wires anywhere in the truck that I can see. It just acts as though something is still turned on. Could the alternator somehow be drawing the juice itself? Would Autozones free test show that or just the fact it charges like it should?

Anybody got any ideas?

[Ranger Dave]

alt.   will  do that. if there  bad.      eather  not  charge  or  draw  when shut off.

voltage reg,  in alt.   

[Bowtie972]

Voltage Regulator inside Alternator bad

[duel1985]

if it is a reman when they assemble them they put a nut on the inside of the altinater which will loosin up an draw   your battery if the two outer nuts do not tightin up u have to take it apart simple cheap fix hope this helps

[TBigLug]

Took it to autozone today and it passed all it's tests with flying colors. I think that will rule out the voltage regulator and rectifier. It is a reman (almost new in fact), where is the nut on the inside? On my wiring diagram it says the red of the two is connected to the ignition switch and the other is connected to the gauge on the dash. Niether wire should have 12 volts in it when the key is off, should it? I think there should only be voltage in the wire coming from the ignition when the truck is running and never in the gauge wire? Or am I totally off kilter on this?

[TBigLug]

Also, I'll try tightening the case screws in the morning and let you all know how it worked out.

[Bowtie972]

An alternator can  still charge the battery and be bad, the regulator will draw voltage after the vehicle is turned off.  You said it yourself in your first post , if the alternator is plugged in it drains it down, when unplugged its ok, theres your answer!

[Hammerlane]

Inside your alt. there are what are called "Diodes"
they work like a one way valve, allowing current to only flow in one direction.
when these go bad...

I would install a different alt. (borrow one if needed) and see what happens

[TBigLug]

I would install a different alt. (borrow one if needed) and see what happens

That;s gonna be the plan next. According to my wiring diagram only one of those wires should have power all the time. The other should only have it in Run or Start. If the borrowed alt. doesn't work I'll probably just reroute the one wire to get the juice only when it should. No time to work on it today but I'll update my progress tomorrow.

[TBigLug]

Turns out you should never second guess your first instinct. The plug was wired wrong. I fished out some wires and reconnected them where they should be. Walla, works like a charm. Thanks for the help guys.