ej25 from 1999 Forester - 3 pin alternator wiring question

[JasonPap2002]

Hi Folks,

 

I have an ej25 alternator wiring question that you may be able to help with.  Essentially my alternator warning lamp is not receiving ground from pin one in the 3 pin connector shown here:

 

 

Wiring in my car is here:

 

 

I can make the alternator warning lamp turn on when I touch the wire going to pin 1 (L) to ground.  My pin 2 (S) is receiving 13 volts (going to B+).

 

Try as I can it seems that pin 1 is open.  However if 12 volts is not on it when started the alternator only puts out 13 volts.  When 12 volts is on it (from the alternator warning lamp wire) then fields excite and it bumps to 15 volts.

 

Any ideas?  I'm beginning to think it's an internal issue - not much else that it can be!  Alternator seems to work fine otherwise...

 

Thanks folks!

 

~Jason

 

 

[Cougar]

Well it seems you have proved the wiring to pin 1 is okay. Manually grounding that wire should turn on the warning light. When the alternator isn't running and the ignition is on then pin 1 should be at ground potential through the alternator circuit and the warning light turned on. It appears that isn't happening so check the voltage on pin 1 with things connected normally and see if you see voltage there. You most likely will since the warning light isn't turning on and something inside the alternator isn't right.

[Fairtax4me]

So the light works, but it doesn't turn on during the bulb test?

[JasonPap2002]

Well it seems you have proved the wiring to pin 1 is okay. Manually grounding that wire should turn on the warning light. When the alternator isn't running and the ignition is on then pin 1 should be at ground potential through the alternator circuit and the warning light turned on. It appears that isn't happening so check the voltage on pin 1 with things connected normally and see if you see voltage there. You most likely will since the warning light isn't turning on and something inside the alternator isn't right.

Cool - I just checked and found that on pin 1 with ignition on I get 5-6 volts.  It must be coming in through B+ terminal because no other wires are connected.  

 

Otherwise it appears the alternator is working fine - putting out 15 volts or more when all wires are connected.  But I really want that alternator light to work!  (I'm OCD sometimes).

 

Anyone know if it's worth opening up and taking a look inside the alt?  Or perhaps I'm missing something else?

 

Pin 1 is the pin closest to B+ terminal, correct?  Grasping at straws here.  :-)

 

Thanks in advance!

[JasonPap2002]

So the light works, but it doesn't turn on during the bulb test?

I think by bulb test you mean touching the alternator warning lamp wire to ground directly (instead of pin 1), and yes it works then...  Really weird issue but slowly pointing to internal alternator issues...

 

~Jason

[Fairtax4me]

Bulb test is when all of the warning lights in the dash turn on when you turn the key to ON. Cel, AT Temp, battery, oil pressure, seatbelt, etc. Some turn on then turn back off after a few seconds. Others the engine has to start before they will turn off.

 

The battery light comes on during the bulb test, then turns off after the engine starts. (If this is how the bulb behaves, the circiut is working normally)

 

If the alternator is not spinning the pin acts as a ground path for the bulb circuit (power flows from fuse box to bulb to alternator to ground). Once spinning, the alternator supplies a matching voltage to the pin which prevents current flow, so the bulb does not light. (Power from fuse box, power from alternator, meet in the middle at the bulb, neither can pass the other, no current flow means bulb is not lit, power struggle ensues, neither has an advantage. Eventually alternator gives up and stops charging after many tens or hundreds of thousands of miles, light turns on)

[Olnick]

Great explanation Fairtax!  I never knew how that worked.  Thanks.

[Fairtax4me]

I learned that from one of Cougar's posts on here quite a while ago.

[JasonPap2002]

Bulb test is when all of the warning lights in the dash turn on when you turn the key to ON. Cel, AT Temp, battery, oil pressure, seatbelt, etc. Some turn on then turn back off after a few seconds. Others the engine has to start before they will turn off.

 

The battery light comes on during the bulb test, then turns off after the engine starts. (If this is how the bulb behaves, the circiut is working normally)

 

If the alternator is not spinning the pin acts as a ground path for the bulb circuit (power flows from fuse box to bulb to alternator to ground). Once spinning, the alternator supplies a matching voltage to the pin which prevents current flow, so the bulb does not light. (Power from fuse box, power from alternator, meet in the middle at the bulb, neither can pass the other, no current flow means bulb is not lit, power struggle ensues, neither has an advantage. Eventually alternator gives up and stops charging after many tens or hundreds of thousands of miles, light turns on)

Thanks for this!  In this case, bulb test is NOT working then.  I get no alternator lamp on when turning the ignition on.

 

I feel that the internals of the alternator are not providing a path to ground when i turn on the ignition.  Its an open circuit and so remains unlit.

 

Anyone know if there is anything inside easily replaceable for this?  Or ?

 

I appreciate all the insight!

 

~Jason

[naru]

Thanks for this!  In this case, bulb test is NOT working then.  I get no alternator lamp on when turning the ignition on.

 

I feel that the internals of the alternator are not providing a path to ground when i turn on the ignition.  Its an open circuit and so remains unlit.

 

Anyone know if there is anything inside easily replaceable for this?  Or ?

 

I appreciate all the insight!

 

~Jason

 

I`ve had bad brushs cause the bulb test to fail on other makes.

[Fairtax4me]

The grounding circuitry for the bulb is built into the voltage regulator.

FSM suggests one of the diodes in the regulator could be bad, but its probably not repairable.

 

The circuit is grounded to the case of the alternator, so it may be worh a shot to ensure that the case is well grounded to the mounting bracket.

[JasonPap2002]

The grounding circuitry for the bulb is built into the voltage regulator.

FSM suggests one of the diodes in the regulator could be bad, but its probably not repairable.

 

The circuit is grounded to the case of the alternator, so it may be worh a shot to ensure that the case is well grounded to the mounting bracket.

 

Thanks!  I tried pushing a grounded wire to the outside of the case but will give a go with wiring it in a bit more solidly.  I have a feeling it's the voltage regulator if this doesn't work.  

 

I hate to put a new alt in there, but what can you do.

 

Thanks again folks!  Any one of you in Austin some time, a beer on me.

 

~Jason

[Cougar]

The alternator case is grounded to the engine so touching another ground to it isn't going do anything. If the alternator is fairly old then fixing just this problem is just basically a bandaid as it most likely needs a whole rebuild. Get yourself a good rebuilt or used replacement unit. That's my advice anyways. It is a lot easier than trying to repair it. Either way the unit has to be removed from the car. Be sure to remove the battery ground wire first before working on the alternator. The main alternator wire is hot to the battery and sparks will fly if it gets shorted to ground with the battery connected.

[JasonPap2002]

The alternator case is grounded to the engine so touching another ground to it isn't going do anything. If the alternator is fairly old then fixing just this problem is just basically a bandaid as it most likely needs a whole rebuild. Get yourself a good rebuilt or used replacement unit. That's my advice anyways. It is a lot easier than trying to repair it. Either way the unit has to be removed from the car. Be sure to remove the battery ground wire first before working on the alternator. The main alternator wire is hot to the battery and sparks will fly if it gets shorted to ground with the battery connected.

 

Good tips!  Yes I agree that a new/used/rebuilt one is where I should go with this.  I do appreciate all of your advice, it's been very helpful.

 

~Jason

[Fairtax4me]

Last time I checked prices for one of these Subaru wanted close to $500 for a reman. The after market places wanted $275-400.

Cheap fix: grab a two wire plug and from a 95-98 and splice that in. The wire for the light is the same, the other two just end up in the fuse box (they may have even joined before getting there IIRC).

Then you can buy the $75 Subaru Reman alternator for the 95-98 Legacy.

 

Bolts right in, works great. Did this on a friends 99 foz a few years ago and its still chugging along just peachy. (And she was thrilled that I saved her almost $400)

[sajaba26@gmail.com]

2001 outback sedan_ I have had the alternator replaced twice now...Alternator 1 month old is not keeping battery charged. Tests at Autozone reveals a voltage regulator problem ... how do i test the wiring connections from the volage regulator to the fuse box etc.

[Cougar]

There should be two small wires going to a connector on the back side of the alternator. Both of those wires should have close to battery voltage on them while the alternator is working. It is also very important that the battery warning light works when you turn the ignition switch to the RUN position. Current passes through that warning lamp to the energize the exciter inside the alternator. That is one of the two wires. The other wire is for the voltage regulator located inside the alternator. As the voltage on that lead goes lower due to increased electrical loads the regulator increases the output of the alternator to balance things out. The voltage across the battery should be between 13.5v to 14.8v while the engine is running around 1,500 RPM and a good load on the system. Another good check to do at the same time is look for excessive AC ripple at the battery. There should be less than 0.1v of AC if the diodes inside the alternator are good. If you check that make sure the meter you are using blocks DC in the AC voltage mode. In the AC mode, the meter will have a zero voltage reading when checking a battery.

 

Another test you can do is check the voltage drop across the main charging lead of the alternator. Check the voltage between the main output lead of the alternator and the positive battery post while the headlights and blower are on full. If that lead is okay you should have less than 0.3 volts across the wire connection. Finally, but certainly not least, is make sure the battery connections are clean and snug tight. Do not over tighten them.