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2001 Forester S auto
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210 Posts
Discussion Starter #1 (Edited)
My headlights were severely dim when I parked tonight, the dash lights come on above 2,000 rpm and then off as soon as it downshifts. The alternator is from a 2006 legacy, it was an upgrade at the time to 110amps from 75amps, and has been running fine now for the better part of three years. What I can't figure out is how the positive terminal wire got so corroded, and burned a hole in the rubber terminal boot. Should I Just get this one rebuilt or buy another used one off fleaBay?


 

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2003 Forester X 5 MT
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523 Posts
You could disassemble the connection and clean it up and then test the voltage at your battery with the car running.

You can also take the alternator to a chain auto parts store and they should be able to test it.
 

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2001 Forester S auto
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Discussion Starter #4
well, my mechanic said that he did tighten the nut, the last time in the summer when they had it in to replace those busted transmission fluid lines. but now it's corroded again? I dont know if it's safe for the good old baking soda and water routine. should I give that a try (disconnecting the battery first, of course)?
 

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2003 Forester X 5 MT
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Just disconnect the cable at the alternator and clean everything with a wire brush (probably safest to disconnect the positive terminal from the battery first). When you put it back together cover the electrical connection with some die-electric grease before covering it up with the cover. You may want to buy a new terminal cover from Subaru $8 if memory serves.
 

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2012 Forester 4 speed auto
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997 Posts
Over charging

Your battery is overcharging since the corrosion is on the positive terminal. If you are undercharging it would be on the negative terminal. Some electrical systems have a battery sensing wire to determine how much to vary the field wires in the alternator to handle the load. There could be excessive resistance on this wire. The best way to diagnosis the problem is use an amp meter to see if the alternator is producing a positive 5 amps at idle. It should not produce too much more.
 

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2001 Forester S auto
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Discussion Starter #7
so, after I correct the problem, does this mean I should switch back to the stock 75 amp alternator (i still have it) ? Or should I invest in a beefier battery?
 

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2012 Forester 4 speed auto
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voltage regulator

If you have optional equipment on your car that exceeds the 75 amps that the stock alternator can produce the battery will discharge. You will need the 110 amp alternator. However, what is causing the alternator to overcharge is the problem. The voltage regulator is the usual suspect. Most regulators are inside of the alternator. Some are separate and attached to the chassis. Whatever setup you have replace the regulator and inspect the wiring.
 

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2001 Forester S auto
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Discussion Starter #9
This is worse than I thought... it pretty much just fell apart with a crackle and a crunch when I unhooked the ring terminal. Can I use off the shelf battery cable for a repair? If so, what gauge wire is needed? The Death Zone Auto parts guy said it would be the voltage regulator if it was UNDERcharging, and possibly the diodes if it was OVERcharging. Is that correct or gibberish? Thanks again for any help guys.

 

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2007 Forester Sports XT 4EAT
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The regulator & diodes are built into the alternator.

They run 2 wires connected in parallel... I'm thinking 10 gauge wires. They connect to the engine compartment fuse box.

If you can find a spot where the wire insulation is not melted, you could splice on to it & add a ring terminal to other end to fit the alternator.

The other option would be to source a replacement cable from a recycler or wrecker.

Bobby...

['07 FSXT MODding Journal] ['03 X MODding Journal]
 

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2001 Forester S auto
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Discussion Starter #11
Thanks Bobby, I thought I would just get the whole length of wire replaced... I'm thinking of OFC copper, maybe an upgrade to 8 awg? I've got a whole spool of 8 AWG red amplifier hookup wire, and I could wrap it in heat shielding, then snake it into the existing loom... what do you think?
I think I'm going to rebuild this alternator. do you know if they made rebuild kits for 2008 Legacy units?
 

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2007 Forester Sports XT 4EAT
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I've never looked at the other end of that cable, where it connects to the fuse box. If the connector is easy to replace, like the ring terminal on the alternator side, then yes, fabricate your own replacement cable. :wink:

I think I'm going to rebuild this alternator. do you know if they made rebuild kits for 2008 Legacy units?
Rebuilding looks involved to me. If you need a replacement, it might be better to source a replacement. :confused:

Bobby...

['07 FSXT MODding Journal] ['03 X MODding Journal]
 

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2003 Forester X 5 MT
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This is worse than I thought... it pretty much just fell apart with a crackle and a crunch when I unhooked the ring terminal. Can I use off the shelf battery cable for a repair? If so, what gauge wire is needed? The Death Zone Auto parts guy said it would be the voltage regulator if it was UNDERcharging, and possibly the diodes if it was OVERcharging. Is that correct or gibberish? Thanks again for any help guys.

Definitely found the root cause of dim lights!
 

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2001 Forester S auto
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Discussion Starter #14 (Edited)
They run 2 wires connected in parallel... I'm thinking 10 gauge wires. They connect to the engine compartment fuse box.

If you can find a spot where the wire insulation is not melted, you could splice on to it & add a ring terminal to other end to fit the alternator.

The other option would be to source a replacement cable from a recycler or wrecker.

Bobby...

['07 FSXT MODding Journal] ['03 X MODding Journal]
Bobby, it appears that the wires are indeed 10 gauge. Now have 4 concerns;

(1). Crimp or Solder?
(2). Same strand count/thickness of new wire section?
(3). Could the wire have melted because the Legacy Alt. was 110 amp versus 70/75 amp stock unit?
(4). Since I'm going with another rebuilt 110 amp unit, would it be a good idea to upgrade the main fuse?
 

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'17 Imp Ltd wagon CVT
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Definitely found the root cause of dim lights!
Bobby, it appears that the wires are indeed 10 gauge. Now have 4 concerns;

(1). Crimp or Solder?
(2). Same strand count/thickness of new wire section?
(3). Could the wire have melted because the Legacy Alt. was 110 amp versus 70/75 amp stock unit?
(4). Since I'm going with another rebuilt 110 amp unit, would it be a good idea to upgrade the main fuse?
If I may,

(1) Always solder, after properly crimping. Then seal the joint with dielectric compound.

(2) Same is OK... as what's there was/is adequate when it is in good condition. Those wires have little conductive copper left, most is copper oxide and have a tiny fraction of their original conductivity.

(3) No... you can have a far more capable alternator, because the source is not what determines current draw, it's the load.

(4) No... again, the fuse is designed to protect the circuit given operating loads. That shouldn't change, and will not be affected by a larger capacity alternator nor any fusing.

Your problem was corrosion, pure and simple. Fix that (and I'd argue the corrosion may have infected the wire well beyond the visible) and install your choice of alternator and you'll be fine.
 

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2001 Forester S auto
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Discussion Starter #16 (Edited)
If I may,

(1) Always solder, after properly crimping. Then seal the joint with dielectric compound.

(2) Same is OK... as what's there was/is adequate when it is in good condition. Those wires have little conductive copper left, most is copper oxide and have a tiny fraction of their original conductivity.

(3) No... you can have a far more capable alternator, because the source is not what determines current draw, it's the load.

(4) No... again, the fuse is designed to protect the circuit given operating loads. That shouldn't change, and will not be affected by a larger capacity alternator nor any fusing.

Your problem was corrosion, pure and simple. Fix that (and I'd argue the corrosion may have infected the wire well beyond the visible) and install your choice of alternator and you'll be fine.
Yes, you may!! :)

I agree with most of your categorical responses to my itemized queries. However, corrosion, "pure and simple" does not strike me as a the sole ROOT cause. The corrosion would need to be caused by something. Internal failures of the alternator seem to make sense like the earlier responses suggest. Furthermore, I have never seen corrosion be a ROOT cause of blackened, charred and brittle plastic, and tear a hole into a very pliable rubber cap for the positive terminal. Don't misunderstand me, I am sure that corrosion was partly responsible, but irregular output of the alternator seems to fit also.
I tried to match the 10awg OEM wire at Death Zone Auto parts, and Oh Really? Auto parts also. Their 10awg was 3/4 size of mine, and their spool 8awg was not only thicker, but had less strands also, so more resistance. I suppose I'll be heading to the Pick and Pull tomorrow...
Thanks for your input about the fuse... saved me a few bucks.

One more question... if I braid the two 10 AWG strands, couldn't I just junction it into say, a single 6 AWG or 8 AWG wire (whichever thickness matches) onto ONE ring terminal??? The top is the OEM dual braided set, middle is OFC 8 AWG 735 strand (very fine). Bottom is also OFC 8 AWG but 165 strand (thicker hairs). What is weird is that both of the red wires are from the SAME manufacturer, same sub-product line, and both CIRCA 1999-2000. Top seems like a deeper reddish copper like OEM, (perhaps same grade of OFC?), but bottom seems more sturdier when twisted, albeit slightly skimpier when compared to the OEM dual braided pair. I know I am delving into finite details, but can someone please humor me?

 

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2007 Forester Sports XT 4EAT
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Normally a crimped connection is acceptable... if you have the correct crimp tool, but personally, I prefer to crimp & solder.

In addition, I would coat the crimped/soldered splice with dielectric grease, followed by 2 layers of shrink tubing. :wink:

More strands = more flexibility. For use where the wire will be subject to mechanical vibrations, I'd opt for more strands.

Bobby...

['07 FSXT MODding Journal] ['03 X MODding Journal]
 

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Discussion Starter #18 (Edited)
Signed, sealed, delivered and relaunched. Thanks to everyone who helped. Now onto the upgraded replacement. Fun fact: Buying a reman. factory spec 70amp alternator specific to 1st gen Fozzies, is MORE expensive than getting a rebuilt 110 amp alternator for a 2008 Legacy...
 

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