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Electrical Demons - Need an Excorsist


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Hello All, new to the forum but not to subaru's. Usually pretty good about figuring things out but this one has me stumped.

 

Problem on my 91 Legacy Wagon:

 

Driving down the road when all my dash lights started turning on when I got below 2500 rpm (not just alt light, ALL lights). I stop and don't see anything burning so I try to make it home. 20 minutes later It's a acting like a dead alternator and losing power so I pull off to take a look. I Try to start it and it starts right up, no dash lights and is running fine? I suspect bad cell in battery and replace it and get home.

 

Next time I drive it its the same thing again. Lights come on on the dash and there seams to be a drain (lights get dim). I check voltage across the battery and it's 12, alternator isn't charging. I replace the alternator.

 

This is where it gets wierd.

 

After I install the new alternator and I finish by connecting the negative terminal to the battery, the power comes on in the car (radio, headlights, etc.). This would all be fine if the key was in, but it wasn't even in?

 

I suspect ignition switch now. So I unplug it. Still everything is on when the alternator is plugged in, I disconnect the alternator plug and all the power goes off, key works and starts the car fine (on battery only).

 

I'm stumped.

 

All help appreciated.

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Hmmm.....something definitely sounds screwy.

 

I don't really see how just plugging the alternator in could cause all that. Did you try and put a voltmeter on the plug for the alternator? The two smaller leads are sense & light, and shouldn't have anything coming from them. The fatter wire is the ignition lead telling the alternator it's ok to "turn on" and make power now. You should have 12v on that when the key is turned to the ignition, and no other times.

 

Check that plug and see what you find out. You've definitely got some sort of wiring issue. I'd look around at all your wires in the engine bay and up under the dash and make sure no animals have chewed through them.

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Something sounds VERY screwy- Did ANYTHING happen before the alternator went dead? wreck, install stereo, or anything else? Looking for cause and effect relationship.

 

Is the new alternator charging properly? And hate to say for sanity check is the Battery of proper polarity and installed correctly-I once bought a New battery and the thing had been assembled backwards inside, the termnal marked positive was actually negative! Drove us nuts until we threw a meter on it.

 

If the alt and battery check out(suspect as they have been changed) , then a short in the wiring harness somewhere or the ignition switch sounds reasonable as far as letting power to the car with the key off. I would wiggle the key on and off to see if there was any change.

 

Anoterh technique to isolate a chort is to pull ALL the fuses out , and replace one by one to see if you can isolate the circuit that is allowing power to enter the car's electrical system. Also, I have not had much problems with my 91 Legacy's Electricals, but is there a relay that is supposed to close when the isgnition is activated that might be stuck in the closed position? I don't know, I'll look at my Chiltons tonight when my wife gets home(the book is in the her car).

 

Let us know further, the gears are clicking on what this could be

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I hadn't touched anything in a long time, the only thing I've done to the car is add remote door locks. I'll check that. Then I'll start pulling fuses, good idea. Battery + and - are on the right leads (I've done stupid stuff like that before...).

 

The white (bigger lead) on the alternator has power going to it even with ignition switch unplugged. So there is something in between the ignition switch and the alt that is feeding power to it. I'll trouble shoot that.

 

I have the wiring diagram from my chilton manual, it's a little hard to follow all the circuits, but it doesn't look like there is a master solinoid.

 

I had a mouse build a nest in the heater box once, but I don't see any signs of nibbling on wires.

 

I haven't even tried to run it with the new alternator because of the wierd power issues (don't want to fry my new alt). The "battery" idiot light never came on by itself when I was having problems. All the dash lights would come on just like when you turn the key before starting (I'm sure something in that circuit is the cause). I know it's not the ignition switch itself though.

 

Thanks guys for all the help and good ideas, I'll let you know what I find out.

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Sounds like we have a good one here. After reading the posts here are my thoughts on this.

 

First, the voltage you saw on the main alternator output lead with everything off, is normal. That lead ties to the positive battery post and it is the line that supplies all the current to charge the battery, which is why it is so large. There is a fusible link in the circuit also if I remember correctly.

 

I assume that the problem occurs when you tie the alternator's main output lead to the main battery wire, is that correct? If so, you may have an internal problem with the diode in the alternator that blocks voltage from backfeeding into the alternator. I would try another alternator since the problem occured after the new one was installed.

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I would check the electrical leads to the ignition switch. It would seem that the incoming leads would have power at all times-and those on the outgoing would only have power after the switch was engaged. If you see power on the outgoing regardless of the key position-the culprit just jumped out. However, if the outgoing leads show fine, then the issue is a cross-over below the switch.

 

Seems to me though it would be the switch. I doubt the alternator could cause power to pass through the switch regardless of switch position.

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Sounds like we have a good one here. After reading the posts here are my thoughts on this.

 

First, the voltage you saw on the main alternator output lead with everything off, is normal. That lead ties to the positive battery post and it is the line that supplies all the current to charge the battery, which is why it is so large. There is a fusible link in the circuit also if I remember correctly.

 

I assume that the problem occurs when you tie the alternator's main output lead to the main battery wire, is that correct? If so, you may have an internal problem with the diode in the alternator that blocks voltage from backfeeding into the alternator. I would try another alternator since the problem occured after the new one was installed.

The voltage is actually on the "plug" (and the main output lead) and everything comes on when that is plugged in (even when the main lead is not disconnected off of the alternator). There are 3 wires that are in the plug, one is a larger white one that has power even when the ignition switch is off (and unplugged). So I'm guessing something is feeding power back through that. Maybe back through the dash warning light circuit? (since all the dash lights were coming on when the problem occured).

 

Tonight I'm going to pull fuses and see if I can isolate a circuit that is the culprit.

 

I'll see if I can test the diodes in the alternator too (the new and the old one).

 

Thanks again for all the help!

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Your welcome for the help.

 

Let me state this again because it is important. The voltage you measure on the large wire of the alternator lead is normal and is not a problem. This wire is the alternator output lead that is tied to the positive battery post and the way it is designed to be. You will be wasting time looking for a problem there. Do not ground this lead with the battery connected or you will blow the fusible link.

 

If the devices you talk about don't have a problem with the output lead disconnected from the alternator I really suggest you try another alternator to see if that will clear things up. Unless I missed something, the problem occured after you connected the new alternator up. I think the reverse blocking diode in the alternator is bad and this will allow voltage to backfeed into the alternator.

 

From your first post:

I disconnect the alternator plug and all the power goes off, key works and starts the car fine (on battery only).

 

This is why I think the alternator is to blame. Things are normal with the alternator disconnected.
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My experience says to check out the grounds. See if you can measure a voltage between what you think is ground and the minus terminal of the battery. Should be "0" volts

 

 

 

Your welcome for the help.

 

Let me state this again because it is important. The voltage you measure on the large wire of the alternator lead is normal and is not a problem. This wire is the alternator output lead that is tied to the positive battery post and the way it is designed to be. You will be wasting time looking for a problem there. Do not ground this lead with the battery connected or you will blow the fusible link.

 

If the devices you talk about don't have a problem with the output lead disconnected from the alternator I really suggest you try another alternator to see if that will clear things up. Unless I missed something, the problem occured after you connected the new alternator up. I think the reverse blocking diode in the alternator is bad and this will allow voltage to backfeed into the alternator.

 

From your first post:

This is why I think the alternator is to blame. Things are normal with the alternator disconnected.

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Your welcome for the help.

 

Let me state this again because it is important. The voltage you measure on the large wire of the alternator lead is normal and is not a problem. This wire is the alternator output lead that is tied to the positive battery post and the way it is designed to be. You will be wasting time looking for a problem there. Do not ground this lead with the battery connected or you will blow the fusible link.

 

If the devices you talk about don't have a problem with the output lead disconnected from the alternator I really suggest you try another alternator to see if that will clear things up. Unless I missed something, the problem occured after you connected the new alternator up. I think the reverse blocking diode in the alternator is bad and this will allow voltage to backfeed into the alternator.

 

From your first post:

This is why I think the alternator is to blame. Things are normal with the alternator disconnected.

Glen, he's not talking about the main lead going to the battery. He's talking about the larger white wire in the plug that goes to the alternator. The newer alternators do not have this ignition lead. That wire should only have power when the ignition is on.

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Got some more info.

 

I wonder if the MPFI diode got messed up. It's tied into the ignition lead going to the alternator.

 

The other thing I could think of after looking at the diagrams is the ECU might be tweaked. You need to do some more testing.

 

Other thing I can think of if the fuse box has some fried stuff some where.

 

Here's some wiring diagrams that should help out a lot.

 

Diode location

http://www.surrealmirage.com/subaru/files/swap/elect_unit_loc/6-3_electrical_unit_location12.jpg

 

ECU I-O

http://www.surrealmirage.com/subaru/files/swap/2-7_ECU_I-O_page1.jpg

http://www.surrealmirage.com/subaru/files/swap/2-7_ECU_I-O_page2.jpg

http://www.surrealmirage.com/subaru/files/swap/2-7_ECU_I-O_page3.jpg

 

Power supply routing (you can see the outputs from the alternator here)

http://www.surrealmirage.com/subaru/files/swap/6-3_power_supply_routing1.jpg

http://www.surrealmirage.com/subaru/files/swap/6-3_power_supply_routing2.jpg

 

Engine Electrical (last 2 aren't pertinent, but to be complete)

http://www.surrealmirage.com/subaru/files/swap/6-3_engine_electrical1.jpg

http://www.surrealmirage.com/subaru/files/swap/6-3_engine_electrical2.jpg

http://www.surrealmirage.com/subaru/files/swap/6-3_engine_electrical3.jpg

http://www.surrealmirage.com/subaru/files/swap/6-3_engine_electrical4.jpg

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Ok Josh, thanks for the notice about that. I assume that there is still a main battery lead connection that is hot at all times (he refers to a white one).

 

I am looking at this statement that Bruce makes:

The voltage is actually on the "plug" (and the main output lead) and everything comes on when that is plugged in (even when the main lead is not disconnected off of the alternator). There are 3 wires that are in the plug, one is a larger white one that has power even when the ignition switch is off (and unplugged). So I'm guessing something is feeding power back through that

He states that the main lead "is not disconnected off the alternator", a different way of saying "when the lead is connected" in my thinking.

 

Since things are fine with the alternator disconnected then it seems that it is problem. I believe voltage from the main lead is backfeeding through the alternator, to the other wires, and turning things on that shouldn't be until the ignition switch is turned to 'run'. I may be wrong, but I think this is what is happening. A simple ohmmeter test of the alternator leads would prove this out.

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Wow, you guys are great. I'll try to take all the advice...

 

What I did now is pull fuses until the mystery power went out (alternator hooked up, ignition switch off). When I pulled the "ignition" fuse, everything went off. There is still power to the alternator, and when I turn the ignition switch on I get power like usual (minus things on the ignition circuit).

 

Looking at the wiring diagrams (thanks) the ignition fuse (fuse 16) is tied to the fuel pump relay, the mpfi control unit, "ALT2" circuit, ignition relay, and the A/T control unit.

 

It looks like the two leads to the alternator should have power at all times (as mentioned) so I still don't think the new alternator is bad (edit: realize that doesn't make sense, I guess that power is normal but the alt. could still be bad). Using a multimeter, the alternator is still only allowing current one direction so I think the diode is ok (I checked the one I pulled out and it was shot). So either the alternator went out and took something with it, or something else fried the old alt. I suspect something else fried the alt. and it's backfeeding power through it.

 

I'll see if I can find the mpfi Diode and I'll check that, I also would like to check the ignition relay but I can't seem to find out where it is?

 

I don't suspect the fuel pump relay or the A/T control unit but if someone think they are suspect I'll see if I can disconnect them.

 

Thanks for all the great help, I'm going out to the garage now to see what I can find.

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Since you have a multimeter handy lets do some testing. I would like to know what the voltage is on all the leads to the alternator, along with the colors of the leads, with the ignition off, and everything connected normally.

 

Another test you can do is remove the alternator lead connections and set the meter to read ohms. Place the red probe lead of the meter, which should be connected to the + of the meter, and connect it to the output lead of the alternator where the white lead would normally tie to. Place the black lead of the meter to each of the other two small wire connection points on the alternator one at a time. Do you get a low ohm reading to either of the small wire connections from the output lead? If you do, then something is wrong in the alternator.

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Since you have a multimeter handy lets do some testing. I would like to know what the voltage is on all the leads to the alternator, along with the colors of the leads, with the ignition off, and everything connected normally.

 

Another test you can do is remove the alternator lead connections and set the meter to read ohms. Place the red probe lead of the meter, which should be connected to the + of the meter, and connect it to the output lead of the alternator where the white lead would normally tie to. Place the black lead of the meter to each of the other two small wire connection points on the alternator one at a time. Do you get a low ohm reading to either of the small wire connections from the output lead? If you do, then something is wrong in the alternator.

Ok Couger, here's what I got:

 

Voltage on the leads to the alternator

 

Main lead:

 

(two big white wires to single screw on terminal) 12.07 Volts

 

Plug:

 

White wire - 12.07 volts

Yellow - 0.00

Black w/white stripe - 0.00

 

Tested ohms (resistance) with positive on the main lead and negative to all other leads on the alt, all tested infinite ohm(no current through). So the alternator should be ok?

 

I tried to find the mpfi diode, but I can't locate it. The diagram says it's near the fuse box under the dash but I couldn't find anything (and I dug around for a long time). If anyone knows what this thing looks like I'd appreciate it. Diagram says it has two wires going to it, one yellow and one Lg (light green?).

 

any other ideas Couger?

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Bruce,

 

Ok, the alternator looks good. I was wrong. Lets see how the voltage is being backfed. What was the number of the ignition fuse you pulled and the lights went out?

 

Edit: When you took the voltage readings was fuse #16 back in place or was it removed at the time? After rereading your previous posts it sounds like that was the fuse that killed the lights, correct?

 

Another thought! Lets take an ohmmeter reading of the two small wires on the alternator but place the common meter lead to ground this time. You may want to disconnect the positive battery lead from the battery before you do this test. Maybe one of these leads is going to ground.

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Bruce,

 

Ok, the alternator looks good. I was wrong. Lets see how the voltage is being backfed. What was the number of the ignition fuse you pulled and the lights went out?

 

Edit: When you took the voltage readings was fuse #16 back in place or was it removed at the time? After rereading your previous posts it sounds like that was the fuse that killed the lights, correct?

The fuse (#16) was back in place when I took readings, and yes that was the one that killed the power (when key was in the off postion).

 

Note, the voltage for the leads I posted was with the alternator disconnected (just taking readings from the wires) did you want me to check them when everything is plugged in? (this would be when power is mysteriosly on and the key is in the off postion).

 

Ok - just did,

 

With the key in the off position and everything hooked up on the alternator there is 12 volts to the white, 12 volts to the yellow, and 1.75 volts to the black with white stripe (and also 12 volts to the main white lead that bolts on).

 

Looked for the diode again, started detaching wire harnesses looking for it and still no luck.

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Ok. Lets pull fuse #16 and then see if you still have 12 volts on the yellow alternator lead. Make sure everything is hooked up normally except for the fuse.

Pulled the fuse and there is still 12 volts on the yellow wire.

 

and... although the radio and lights don't come on with fuse #16 pulled and the key in the off position, I could hear a few solinoids still click when I plugged the alternator in???

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Well then, it does indeed sound like the alternator is backfeeding the voltage to the other things.

Yea, I guess so? Well, I'll try taking back the alternator (should be a fun one, they don't like taking back alternators...) and I'll get another one.

 

Hopefully that will solve my problems.

 

Thanks for all the help, I'll let you know what happens...

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Your welcome for the help.

 

Hopefully you can get another one. Keep us posted on the progress. I would use the same thread.

Well, out of curiosity I checked my mother in laws subaru to see what had power and what didn't and the yellow wire has power when the key is off as well. So now I'm thinking that maybe my new alt isn't bad (seemed unlikely anyway)

 

Looking at the wiring diagram I still suspect the mpfi diode, but I can't seem to find it. If anyone knows where it is (or at least what it looks like) I'd love to know. The diagram that was posted show's it right near the fuse box under the dash but I can't find anything that even looks close...

 

Still open for ideas on what to check next...

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In order to prove the alternator is bad you may be able to do a little test. Try placing a test light probe between ground and the yellow lead of the alternator (don't use your meter for this test). Leave everything connected with the ignition off. I suspect the light will glow on your alternator and not on your mother-in-laws. If that is the case, you need a new alternator.

 

You could be correct, that one of the diodes is shorted and not blocking the voltage to where it should be. I don't think it would be the MPFI diode because that one is forward biased with voltage coming from the alternator direction.

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In order to prove the alternator is bad you may be able to do a little test. Try placing a test light probe between ground and the yellow lead of the alternator (don't use your meter for this test). Leave everything connected with the ignition off. I suspect the light will glow on your alternator and not on your mother-in-laws. If that is the case, you need a new alternator.

 

You could be correct, that one of the diodes is shorted and not blocking the voltage to where it should be. I don't think it would be the MPFI diode because that one is forward biased with voltage coming from the alternator direction.

Ok I'll go check it. I did find the elusive diode and it still functions just fine so I can check that off the list.

 

While I was under the dash I noticed the green led on the ecu blinking, three blinks, pause, three blinks, pause, ....

 

Not sure if that indicates anything?

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