TheSubaruJunkie Posted December 31, 2008 Share Posted December 31, 2008 (edited) So my Brat stopped charging today. Im looking over the wiring that was kinda hacked and put together on this thing. The previous owner removed some of the original wiring and put his own. He has a fuse block under the hood with four fuses. The aftermarket fuse block is powered by a relay that supplies 12V from the battery when the ignition is on. So one of those fuses leads to the alternator plug. The other goes into the stock harnes. but it's apparent both wires were spliced at one point in time. The stock harnes has two wires. A tiny red, and a larger white. The White, from what i understand, is the switched 12V to excite the alternator. The smaller wiring leads to the dummy light in the dash. What I have here is, the large white wire goes into the plug, the small red wire goes nowhere. The other spade on the plug goes to the 12V on the aftermarket fuseblock. This is where the confusion begins. Which post on the plug gets the 12V from the harness??? and which gets the small wire for the light? What tells the dummy light to illuminate?? The fuseblock keeps blowing a fuse. it did this in the past, i replaced the fuse and the alt charged again no problem. Today, all it does is blow fuses. I'm near positive the alternator is bad. However, I want to re-wire this the correct way but not really sure where to begin. I used to have a EA81 FSM but I gave it away. Ive looked high and low, and cannot find any wiring diagram for the EA81 anywhere. HELP Edited December 31, 2008 by TheSubaruJunkie Link to comment Share on other sites More sharing options...
Cougar Posted December 31, 2008 Share Posted December 31, 2008 I think the plug on the back of the alternator should have two pins. One is for the regulator and the other is the lamp lead to the dash. Both leads should have 12 volts on them when the ignition is ON and engine is OFF. To see if the alternator is causing the fuse to blow, remove the leads going to it and try another fuse. If it doesn't blow the problem is the alternator. Be carefull working with the main lead to the alternator as it is always hot to the battery. Disconnecting the battery ground lead is a good safe practice when working on the alternator. Link to comment Share on other sites More sharing options...
TomRhere Posted December 31, 2008 Share Posted December 31, 2008 http://mshoup.us/docs/fsm/EA81/83/ Link to comment Share on other sites More sharing options...
TheSubaruJunkie Posted December 31, 2008 Author Share Posted December 31, 2008 I think the plug on the back of the alternator should have two pins. One is for the regulator and the other is the lamp lead to the dash. Both leads should have 12 volts on them when the ignition is ON and engine is OFF. To see if the alternator is causing the fuse to blow, remove the leads going to it and try another fuse. If it doesn't blow the problem is the alternator. Be carefull working with the main lead to the alternator as it is always hot to the battery. Disconnecting the battery ground lead is a good safe practice when working on the alternator. We've already verified the Alternator is blowing the fuse. So BOTH pins need 12volts with the ignition on? Right now, the white wire has 12v constant, the other wire gets 12v switched. Link to comment Share on other sites More sharing options...
TheSubaruJunkie Posted December 31, 2008 Author Share Posted December 31, 2008 Thanks Tom for that link!! I was looking at the wiring diagram... and if I'm reading this correctly, then the large white should have a constant 12v?? Here's a copy of the diagram, with some wires traced.... It appears the two wires off the alternator, labled B & S come straight from the Fusable Link, which is connected directly to the battery. No switches. Then it shows wire labled L goes to the fuse block, leading to the Charge Indicator Lamp. Anyone know what this WR listed in that circuit is? Is it some sort of regulator? If its leaving the alternator, and headed to the lamp how would it be getting 12v?? Does the lamp send 12v current from it, through the block, to the alt??? Or is it the other way around... alternator sends 12v to the fuse block? Im already 100% positive my alternator is junk. I just dont want to replace it and have this problem come back up cause of some shoddy wiring. Link to comment Share on other sites More sharing options...
TheSubaruJunkie Posted December 31, 2008 Author Share Posted December 31, 2008 Okay. Im talking to the guys here at work. (all certified & highly trained service tech's) and every one of them is telling me the light indicator should be a ground and NOT a 12v source. Alittle more sifting through the FSM reveals this which confirms their beliefs: What this diagram here shows me is the alternator provides a common ground for all dash indicators. With each having a seperate sensor to provide ground if that feature fails. If the alt fails, it provides a ground for ALL indicators... which, from previous experience, is what happens when the alt dies (all dash indicators illuminate). Somebody please correct me if I am wrong. Link to comment Share on other sites More sharing options...
Cougar Posted December 31, 2008 Share Posted December 31, 2008 Since you have 12 volts on both wires you should be good. You have proved the alternator has an internal short so you need to replace it. When you install it and repair the wiring things should work ok. The wht/red wire has voltage applied to it and it runs through the battery warning light to the alternator field circuit. This circuit provides current to the exciter circuit in the alternator so the field can build up to produce the output of the alternator. Many years ago I learned the hard way about the warning light. If that light doesn't turn on when you turn on the warning lights there is no charging from the alternator. When the alternator builds up a charged field then the lead going to the w/r wire will have a 12 volt backfeed to the warning light. This will cause the light to go out, as it should when the alternator is working like it should, since there will be no difference of voltage across the lamp. Link to comment Share on other sites More sharing options...
TheSubaruJunkie Posted December 31, 2008 Author Share Posted December 31, 2008 The wht/red wire has voltage applied to it and it runs through the battery warning light to the alternator field circuit. This circuit provides current to the exciter circuit in the alternator so the field can build up to produce the output of the alternator. Many years ago I learned the hard way about the warning light. If that light doesn't turn on when you turn on the warning lights there is no charging from the alternator. When the alternator builds up a charged field then the lead going to the w/r wire will have a 12 volt backfeed to the warning light. This will cause the light to go out, as it should when the alternator is working like it should, since there will be no difference of voltage across the lamp. I maybe niaeve, but none of the schematics I am looking at backup your claims. Im not calling anybody here a lair, i just want to try and understand this and what I am being told is not being proven on paper. Link to comment Share on other sites More sharing options...
Cougar Posted December 31, 2008 Share Posted December 31, 2008 What I told you is correct. If you don't believe me then you will have to trust me on that. I have to go catch a flight right now and do have time to explain further. I will try to get back to you on this later. Link to comment Share on other sites More sharing options...
TheSubaruJunkie Posted December 31, 2008 Author Share Posted December 31, 2008 What I told you is correct. If you don't believe me then you will have to trust me on that. I have to go catch a flight right now and do have time to explain further. I will try to get back to you on this later. I really apreciate the help Cougar, im not trying to disprove you. Just looking for evidence in the schematics to help. Ive been trained to read electrical (and hydraulic) schematics, and tend to trust the manufacturer on this one. If I had another EA81 to use as a template or for Trial & Error, it would be helpful. The wiring on this car is so hacked I cannot trust any of it. Link to comment Share on other sites More sharing options...
Skip Posted December 31, 2008 Share Posted December 31, 2008 Brian, Cougar is correct the wire color he mentions as white with red is the "L" terminal of your first diagram, lower wire on your second diagram The alt function happens as both of you describe. When the alt has and output the voltage from it cancels (so to speak) the ground you mention. Sort of off setting penalties if you will. When the alt goes toast (i.e. no output) the ground wins and all lights on the circuit come on. Bet that makes it clear as chocolate milk BTW your second post has the "S" terminal (white wire) missing. Link to comment Share on other sites More sharing options...
TheSubaruJunkie Posted December 31, 2008 Author Share Posted December 31, 2008 Bet that makes it clear as chocolate milk BTW your second post has the "S" terminal (white wire) missing. Sure does. So you are saying the output from the W/R wire is feeding 12V. When it malfunctions it then creates a ground and illuminates the dash lights? That makes sense. So with my hacked up wiring, i should be able to take the original W/R wire (which right now has been cut) and if I ground that, all my warning indicators should light up?? Link to comment Share on other sites More sharing options...
Skip Posted December 31, 2008 Share Posted December 31, 2008 "So you are saying the output from the W/R wire is feeding 12V. When it malfunctions it then creates a ground and illuminates the dash lights?" That pretty much sums it up. I don't like the "when it malfuctions" part. When there is no output on the L terminal (W/R) wire be it that the engine isn't running or the alt output has "ceased to be" then the ground appears and the lites all light. "So with my hacked up wiring, i should be able to take the original W/R wire (which right now has been cut) and if I ground that, all my warning indicators should light up??" Yep, if it is connected as shown in your second diagram that should be the case, mate If the lamps are there and good that is. (DO not ground the part of the wire connected to the alt!!) Link to comment Share on other sites More sharing options...
TheSubaruJunkie Posted December 31, 2008 Author Share Posted December 31, 2008 Ok Great. Thanks to the both of you, Cougar & Skip! I think im finally getting this. So now the next question.... ... should I be supplying 12V to that L terminal? Currently, there is an aftermarket fuse block that is switched 12V that leads to that terminal. The original W/R wire is cut and goes nowhere. I have a replacement alternator now, and when I put it in, i want to make sure I dont risk blowing it up. Link to comment Share on other sites More sharing options...
Skip Posted December 31, 2008 Share Posted December 31, 2008 Here is your second diagram with the missing notations (hope you don't mind me pirating your schematic) Comparing this to your first diagram you should now see the "L" terminal gets the wire (W/R) from the dash lights the "S" terminal (W) gets +12 V all the time as does the heavy W wire connected to the "B" terminal Let it also be seen what Cougar warned about both white wires are always hot. Either wire to ground will blow the fusible link #2. Link to comment Share on other sites More sharing options...
TheSubaruJunkie Posted December 31, 2008 Author Share Posted December 31, 2008 No worries Skip. The diagram originally belongs to Subaru (FHI). I hope they dont mind. Now that I understand how all the wiring works, i'd like to know if I should just disconnect the W/R wire all together... since he has 12V rigged to goto that wire at this time. Is that even necessary? Of course, I would like to revert everything to the original wiring. If the dash wiring is still correct, I will attempt that. There is alot of wiring on this car that is altered. And half the dash doesnt even work (no open door indicators, headlight indicator etc) So im sure if I connect the original W/R wire, i will get nothing. Does the Alt care about that? Or will it work regardless? Link to comment Share on other sites More sharing options...
Skip Posted December 31, 2008 Share Posted December 31, 2008 No worries Skip. The diagram originally belongs to Subaru (FHI). I hope they dont mind. Kewl and you're welcome for trying to make it so you would understand it. Now that I understand how all the wiring works, Well then why the questions?? i'd like to know if I should just disconnect the W/R wire all together... since he has 12V rigged to goto that wire at this time. Is that even necessary? Wait now wait you just said Now that I understand how all the wiring works, I have lost my touch at explaining things I give up ask Cougar. So im sure if I connect the original W/R wire, i will get nothing. Does the Alt care about that? Or will it work regardless? How can you be sure if you haven't tested it? I give up ask Cougar. Link to comment Share on other sites More sharing options...
TheSubaruJunkie Posted December 31, 2008 Author Share Posted December 31, 2008 Sorry skip. Im doing all this at work right now. I get off in 20 minutes and when I get there I can get my hands dirty and try everything out. It would be easier i guess if I were at home and could run out and check things. Just want to make sure things are not going to break and leave me stranded.... again. Link to comment Share on other sites More sharing options...
GeneralDisorder Posted January 1, 2009 Share Posted January 1, 2009 It's really quite simple Brian: The large white wire and the smaller white wire both go to the fusible links - otherwise known as the "main junction". The large wire is the alternator output, and the smaller one is the sense wire used by the alternator to adjust the voltage output at the main junction. The last wire (white/red) is primarily the feild excitation source, but also functions as a sort of malfunction indicator as the 12v supply is routed through the charge indicator lamp. When the alternator is producing no power the feild windings act as a ground and power flows through the lamp. When the alt is functioning there is potential on both sides of the lamp - if the output drops to lower than battery voltage the charge indicator will again illuminate. Incidentally, the feild excitation wire is not needed. The alternator will self-excite once it reaches a fast enough speed. But it does sound like you have some serious rewireing to do in order to make it work as stock. GD Link to comment Share on other sites More sharing options...
Cougar Posted January 2, 2009 Share Posted January 2, 2009 The diagram in post #6 shows a simplified circuit of what we are talking about. As you see, the lead from the charge light goes through a isolation diode and to the alternator 'L' lead. When the key is ON and the engine OFF (KOEF), the voltage on the W/R lead at the alternator will be near zero volts (ground potential), lights ON. When the good alternator is running that lead will be near 12 volts and the lamps will turn off. Put the replacement alternator in and measure the voltage. You will see what I am saying. To see if the W/R wire at the alternator is working like it should remove it from the alternator and just touch the lead to ground. The warning lights should turn on. Link to comment Share on other sites More sharing options...
TheSubaruJunkie Posted January 2, 2009 Author Share Posted January 2, 2009 Yeah i tore into it today. The W/R does nothing for my dash. So i took the gauge console out, and its a disaster in there It looks like im going to need a new wiring harness cause the Prev. Owner completely hacked everything in there. Ontop of that, the new alternator from NAPA was the wrong one. Looks identical, but the mounting ears are 1/8" narrower than the original. Lucky for me I had a spare alternator hiding in my garage... so I bolted that up. The white wire (s) has 12V but the alternator was not producing power. Once I supplied 12V to the other wire, it the alternator started to work. So I got some pix of the connector and im going to look over them and compare to the wiring diagram and see what is what. Link to comment Share on other sites More sharing options...
Cougar Posted January 2, 2009 Share Posted January 2, 2009 If you can find the end of the w/r wire coming from the dash you can run a wire to that pin on the alternator and hopefully that will solve that trouble. Perhaps though the wiring is more mangled than I imagine and that isn't going to work. Link to comment Share on other sites More sharing options...
TheSubaruJunkie Posted January 2, 2009 Author Share Posted January 2, 2009 Yeah, things are bad. It appears the car used to have a digital dash, and this was an attempt to convert it to analog. Link to comment Share on other sites More sharing options...
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