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Unread 10-25-2013, 12:02 PM   #1
chaddube
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1987 YJ Wrangler 
 
Join Date: Oct 2013
Location: black canyon, az
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87 yj alternator not charging and getting hot

so trying to make a long and frustrating story short Ill try to give an overview- alternator threw a belt- replaced belt and realized the alt was getting red hot after only mere seconds of running- tested alt--tested good but bought a new one anyway- replaced alt- still getting super hot and not charging- after days of poking around- looking for a short or something my mechanic neighbor suggested to connect one of my hot wires and the exciter wire- it worked- started charging and no more hot- after bout 2-3 months of flawless performance it did it again- - read about every forum and still cant seem to lick this one- help - its been 80 degrees in phx and every weekend I see jeepers out- WITHOUT ME

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Unread 10-25-2013, 03:24 PM   #2
Que89YJ
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1989 YJ Wrangler 
 
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Location: Detroit, Michigan
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So the exciter write was jumped to the hot lead from the battery & hot all the time?
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Unread 10-26-2013, 02:43 AM   #3
chaddube
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Quote:
Originally Posted by Que89YJ
So the exciter write was jumped to the hot lead from the battery & hot all the time?
No. The plug that plugs into the alt was just spliced together leaving the original exciter taped off
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Unread 10-26-2013, 09:53 AM   #4
Que89YJ
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1989 YJ Wrangler 
 
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So we are on the same page here are the links to the fsm:
To download the fsm:
http://dl.dropbox.com/u/40590346/87-88%20YJ%20Jeep%20Wrangler%20FSM%20manual.pdf
http://dl.dropbox.com/u/40590346/1990%20Jeep%20Factory%20Service%20Manual.pdf

You have the 2 red wires and the tan wire. You cut the smaller red wire and just jumpered it to the battery wire. Does it get hot while just setting there before running the engine?
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Unread 10-26-2013, 11:22 AM   #5
chaddube
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Quote:
Originally Posted by Que89YJ
So we are on the same page here are the links to the fsm: To download the fsm: http://dl.dropbox.com/u/40590346/87-88%20YJ%20Jeep%20Wrangler%20FSM%20manual.pdf http://dl.dropbox.com/u/40590346/199...e%20Manual.pdf You have the 2 red wires and the tan wire. You cut the smaller red wire and just jumpered it to the battery wire. Does it get hot while just setting there before running the engine?
Not hot while sitting. Actually show a drop in amps at the alt when started. If I disconnect everything and test the alt by itself it's good. No heat and pushing 14 volts. I'm convinced it's got to be a short somewhere or not grounded correctly but I can not find it.
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Unread 10-26-2013, 03:02 PM   #6
Que89YJ
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1989 YJ Wrangler 
 
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You pulled the alternator and had them load test it?
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Unread 10-26-2013, 03:35 PM   #7
chaddube
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[QUOTE="Que89YJ"]You pulled the alternator and had them load test it?[/QUOTE

Yes alt is good. Both of them.
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Unread 10-26-2013, 03:41 PM   #8
chaddube
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Quote:
Originally Posted by Que89YJ
You pulled the alternator and had them load test it?
And I've tried them both several times with the same result. At one point the alt would charge at 1200 rpm then not charge again after I dropped below that point even if I reved the engine above 1200. Definately wiring just not sure where. I did the nutter bypass a while ago. Wondering if hooking it back might help. All my jeep buddies are stumped. Thought about a new harness but hate to find out after that it was a loose wire or a bad relay
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Unread 10-29-2013, 04:12 PM   #9
JWELK
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When it gets hot that indicates a short. Does it get hot with engine off and key in "run"? The alternator output goes to the PDC, which is all fused, the battery and starter, the latter 2 are supposed to have fusible links, but may have been replaced with standard cable. Sooooooooooo. It is possible the short is internal to the alternator. I find it interesting the engine runs when the alternator gets hot and is not charging. That means it is running on the battery, how long has it run in this condition before you stopped and felt the alternator?
I think we're going to need a bit more info to steer you in the right direction.

Regards,

Jim W
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Unread 10-29-2013, 04:31 PM   #10
Que89YJ
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1989 YJ Wrangler 
 
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I think he is a tbi with fuseable links
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Unread 10-29-2013, 07:19 PM   #11
chaddube
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Quote:
Originally Posted by JWELK
When it gets hot that indicates a short. Does it get hot with engine off and key in "run"? The alternator output goes to the PDC, which is all fused, the battery and starter, the latter 2 are supposed to have fusible links, but may have been replaced with standard cable. Sooooooooooo. It is possible the short is internal to the alternator. I find it interesting the engine runs when the alternator gets hot and is not charging. That means it is running on the battery, how long has it run in this condition before you stopped and felt the alternator? I think we're going to need a bit more info to steer you in the right direction. Regards, Jim W
Interestingly enough the jeep will run with the negative removed from the battery. Although it sounds distressed when I do this. --- my previous setup was alt output and 1 other hot wire running to my starter sylonoid and my brown excite wire running to my harness. Assume it's to the ignition. Ok so here is where we start. I broke the alt belt. After replacing it I noticed the heat from the alt. I assumed this is why the belt broke to begin with. After not being able to find the problem my neighbor suggested to connect the hot wire and the excite wire together. This will fool the alt into charging. Ok so I tried it and it worked. No more heat and it was charging. After a few months of flawless perfmance I had gotten winched out of a tight spot then drove it home. Next day I realized it was not charging again so I popped the hood and found the alt hot again. I'm not an electrical guy so that's why I'm reaching out to the jeep land. I have had both alts checked and they are good. Batt is good. The alt does not get hot with key in start position only when running. And it produces 14.4 when not hooked up. But drops to 11.5 when connected
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Unread 10-29-2013, 07:46 PM   #12
dancytron
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Could be a short at the starter relay (on the firewall below the battery, follow the small positive battery cable)??

Find that, take all the wires off the post, see if there is any sign of burning and clean them up.

That's where the fusible links are too. Maybe someone put a regular wire in place of a fusible link and it is jumping to ground somehow? A lot of people (including me) have problems with that connection not conveying enough power and bypass it, but that just makes the battery not charge, I don't think it makes the alternator get hot.
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Unread 10-29-2013, 07:52 PM   #13
chaddube
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All fusable links are in place and don't appear to be burnt. Is it possible it's in the ignition somewhere? I've heard about bypassing this by putting in a diode and running the excite directly to the coil
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Unread 10-30-2013, 07:18 AM   #14
Que89YJ
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The alternator is self regulating. There is no external input to fool to make it charge. If you have power on the input then you have a wire problem if you don't see an output. Check power at the alternator side of the wire. See if you get anything out there. The alternator wiring is pretty basic. Check the voltage on the original exciter wire, the jumper you installed and the main output. Post what you find.
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