I have a 1982 Datsun 720 diesel engine SD22. 4 Cylinder orange rusted POS that I love very much. Although she tried to kill me today. I am replacing the alternator and my battery started to smoke and I thought it was going to explode... I disconnected everything. I hooked it up according to the way it was before... Does anyone have any idea what is going on. I think its not connected right but I don't understand what is incorrect. What are the connections? I need to understand completely what wires are what and what the alternator's different connectors are. I am testing the battery, which is still under warranty. I am also tracing every wire and checking every ground. But can anyone explain the back of the alternator and its connectors? I will post a picture... Thanks in advance...

https://www.flickr.com/photos/128925928 ... ed-public/

This is the back of the alternator...

It's kinda hard to mess that up, you have 3 things to connect, the plug, the main wire to the output post, and the ground wire, that's about all there is.
Have you bypassed the fusible links, they are the black and green wires that come off the positive post.

When did it start getting hot, when you put the positive cable onto the battery, when you plugged in the plug, or when you connected the main wire to the alternator under the plug?
Which wires got hot/burnt up/caught fire?

scottfelsen wrote:https://www.flickr.com/photos/128925928 ... ed-public/

This is the back of the alternator...

that is not a stock alternator rig, is it?

The wires did not get burnt up but the battery started to steam and it looked like it was going to explode. The plug going into the alternator is different. I have two wires going into the alternator and the alternator has three prongs that the plug (with the two wires) plug into. That's why I am trying to figure out what the connections are on the back of the alternator... What are the three prongs coming out of it and what are the two wires on the plug comming from the wiring harness. Obviously there is an issue here... lol

Correction, One of the fusible links connected to the positive side of the battery is burnt out it is one of the wires going to the plug on the alternator. Its the bottom pole. So that narrows down the issue. But where does this actually get connected? I believe the plug and the new alternator do not connect so I need to figure out where these wires do connect and make those connections... Any one know anything that could help... lol If I don't survive this... It was nice knowing ya...

I would just put the vacuum pump on the alternator that you had in it, just mount it carefully, and then call it good, that is what I would do.
I don't think you can get a new fusible link harness anymore, I put a blade fuse plug in the one I have, I am not the one that screwed it up, this was just my fix, don't know if it will work the same as the fusible link, but it's got to be better than deleting it entirely.

scottfelsen wrote:Correction, One of the fusible links connected to the positive side of the battery is burnt out it is one of the wires going to the plug on the alternator. Its the bottom pole. So that narrows down the issue. But where does this actually get connected? I believe the plug and the new alternator do not connect so I need to figure out where these wires do connect and make those connections... Any one know anything that could help... lol If I don't survive this... It was nice knowing ya...

According to my 1982 Datsun PU wiring diagram for a diesel engine there are only two wires coming out of that plug on the alternator where you have 3 wires on that alt, one is white, the other is white/blue, the white goes to one of the fusible links among many other things(DPC, fuse block, the main output wire, ect.), and the white/blue wire goes to a resister, the glow plug timer, and the charge light.
Remember that there is a main black wire that goes from the alternator housing to a main body ground.

Here is your photo of the alternator and plug.
Alternator by Scott Felsen, on Flickr

Thanks. I now have to figure out what you just said... lol... I do appreciate it though...
I do have two wires on my plug from the battery and three on the alt. Plus the ground which I think is listed E on the pic above and the pole screw which is directly below the plug... I think I know where the ground goes, and where the wire that connects to the pole screw goes. The other two... I am confused still....

I replaced the fusible links with other fusible links. Not exactly the same but it will do the same thing. Your fuse should work as well. I like it better since there won't be any rewiring if the fuse blows...

I did it that way because the former owner just shoved the burnt off wire into the fusible link wire next to it, so double the power had to go thru that fusible link, and it also kept falling out.
Like I said, I would just mount the vacuum pump on the other alternator you have with the two wire plug, it's just easier that way.
I will ask again, which wire almost or did catch on fire, that wire could possibly tell you a lot.
Have you added any wires?

scottfelsen wrote:I replaced the fusible links with other fusible links. Not exactly the same but it will do the same thing. Your fuse should work as well. I like it better since there won't be any rewiring if the fuse blows...

The old alternator wasn't working... Its gone. The wire that burned up came from either the pole or from one of the wires on the plug that goes into the alternator. I get continuity from both of them to the end of the positive battery cable... I am not sure what is normal in continuity testing on these wires...

Never ever throw away a diesel specific part, don't turn them in as cores either, starters and alternators get rebuilt as they are hard to find when you need them.
I thought that you were the member here that had to find another Vacuum pump that got broken when you were mounting it onto your rebuilt alternator, and then you found this alternator with the vacuum pump on it, what happened to that alternator, why can't you mount the vacuum pump on that alternator?

OK, this is how the wires have been explained to me, the solid white wire in the plug is connected to a keyed source of power from the fuse block, it basically turns the alternator on, when you turn the key off while the engine is running, the power is turned off which turns the alternator off, that is why the light comes on until the engine quits turning, as it is not creating power anymore.
The white/blue wire that goes to the light in the dash has power on both ends, the light gets power from the fuse block, and the alternator supplies power also at its end while it is running, so if the alternator fails, then instead of that end of the wire having power, it becomes a ground which allows the light to come on telling you the alternator is not making power anymore, the light will not come on when it has a power source at both ends.
The main output post on the alternator is connected to the battery in some way by a larger wire, it charges the battery when the alternator is being turned by the engine, sometimes to clean up the engine bay, guys will connect the white wire from the plug directly to this main wire as it has power all the time, so the moment the alt starts turning it creates power because it is excited all the time as it is connected straight to the battery, for some reason it does not drain the battery wiring it this way.

This is all I know about about the alternator, I do have a 3 wire alternator myself, but it is not like yours, and I don't have the original plug with 3 wires to look at the color of the wires, mine has a regular plug hole, it's not like yours where the wires come out of the alt to a plug, mine the extra wire is automatically deleted, it just has no wire going to it but the plug still inserts into the hole.
Here is my plug, it looks like the upper right of the plug is deleted(no wire, upper left hole in this photo from this angle).

Here is the alternator 3 plug hole, upper right spade is deleted.

Here is my 2 wire plug, no upper right spade/wire.

Maybe this will help you, maybe it won't, I did pull out my 1985 diesel harness to see if that part of the harness was in the box, it was not in the box which kinda depresses me because it is not complete.

scottfelsen wrote:The old alternator wasn't working... Its gone. The wire that burned up came from either the pole or from one of the wires on the plug that goes into the alternator. I get continuity from both of them to the end of the positive battery cable... I am not sure what is normal in continuity testing on these wires...

Yes the alternator was bad and the replacement came without the vac pump and while putting on the vac pump it broke. lol Yes I shouldn't have thrown out the old alt... But I have replaced it before without any drama . I just did 30 pushups as a punishment... lol Thank you very much for your help. I think your info will be needed. I need to figure out what the wires are coming from the plug on the alternator. I have called the manufacturer and they haven't returned my call... Surprise!!! Right now I am ripping the wiring harness apart checking for shorts. I have already found a few bare wire spots I am taping up. I have never done this before... But I am learning... I think I may have a short because when I tested continuity between the ground wire and the positive battery cable I got continuity briefly... I think there may be a short. If not... It's a great time to waste a day chasing the wires.

Finally got everything connected and working correctly. Thank you for your help!!! Now I just need to build a hydraulic hose for the oil vacuum pump on the back of the alternator. Mine failed when I reconnected it to the alternator and engine block. Is my truck cursed?

Yea, that hose can be a hassle, I have broken one of them myself, take your broken one to a shop that makes hoses and have them make you one from your sample.