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Alternator upgrade Do I need to add a wire going from the ALT to the battery positive terminal?

post #1 of 7
3/5/13 at 12:20am
Thread Starter 
I'm upgrading from a 75amp (PN: 23700-AA430) alternator to a 110amp (PN: 23700-AA570) alternator.

Do I need to add a fused link from the alternator to the battery. so I don't blow the 80 amp main fuse? And if so what gauge wire and amp fuse do I need?

Car: 2005 Subaru Impreza WRX

Back story: I added a 400RMS sub and amp to my car and started to experience my lights dimming. I upgraded my battery to a DieHard Platinum and that took care of the light dim but not permanently. After 20-30 minutes of playing the stereo loud the lights will start to dim again. I went by o'reilly auto parts and had them test the alternator/amperage at the battery with stereo off, then with the stereo on. Stereo off it had 38 amps at the battery stereo on at 50% volume playing some Sublime it dropped to 13 amps and their machine said low output. The oem WRX 75amp (PN: 23700-AA430) alternator is not cutting it. So I ordered a 06 STI 110amp (PN: 23700-AA570) alternator that I found on eBay.

Thanks for looking, reading, and leaving your thoughts.

Notes: Original thread that lead to purchasing the new alternator http://www.avsforum.com/t/1460033/lights-are-dimming-when-my-sub-hits-is-400-rms-too-much-details-in-side#post_23021146
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post #2 of 7
3/5/13 at 6:02pm
Here's a wire chart which will help you:
http://www.rallylights.com/hella/SensibleWiring.aspx

And yes... you will have to get rid of the 80 amp fuse. You MAY not have to add any link though depending on the gauge of wire on your 80 amp main. Check it against the chart. It may be as simple as splicing in a 120 amp fuse directly in place of the 80. If the existing wire is too small though then you will have to slide a larger fuse in between the battery and alt.
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post #3 of 7
3/5/13 at 6:28pm
how would adding a fused link prevent the 80 amp fuse from blowing?

I have never heard of running fused wire from battery to alternator....this must be some new safety thing? so you dont blow up your car if you try jumpstarting it with crossed wires?

i think i woudl vote no on adding fused wire....but i am not an electrical expert by any means.
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post #4 of 7
3/5/13 at 7:04pm
Quote:
Originally Posted by tundrSQ View Post

how would adding a fused link prevent the 80 amp fuse from blowing?
.
You're basically bypassing it with a fused link directly to the battery, so it doesn't matter if it blows or not. In fact with a fuse link between the alt and bat you should be able to pull the 80 amp fuse altogether and leave it empty.
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post #5 of 7
3/5/13 at 10:51pm
Actually many car manufactures did and do just that in the wiring harnesses or on and under the relay boards sometimes at battery/ starter connection They started that in the 70's before that they just let you wait till the car caught on fire or if you were lucky a diode plate or stator wire melted open in the alternater opening the ground path first .
GM and others AMC/Jeep and Ford usually did a similar thing bit at the external starter sol. for years GM had the alt batt wire connect at the batt/starter terminal with a short link of fuse link at the starter then up to the alt harness. The Japanese usually pit there fuse links on the relay board until they started using main fuses . It used to be common to diagnose and open circuit by pulling on the fuse link wire if you knew where it was and if
stretched easily like taffy you knew the wire was open inside .
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post #6 of 7
3/10/13 at 5:54pm
Thread Starter 
I added some grounds and a 100 amp fused bypass for the new alternator, that I put in.
I will be getting some loom for the grounds, so every thing's not red.

The Scosche wiring kit that I got came with a .5 farad Cap so I put it in.

I'm not really sure if it's doing any thing, but the sub is hitting hard enough that I'm going to have to take the headliner out when its nice out and put some foam on the inside of the roof so it doesn't vibrate.
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post #7 of 7
3/16/13 at 11:20am
can't go wrong with good grounds that's for sure
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AVS › AVS Forum › Other Areas of Interest › Car Audio, Video, and Nav › Alternator upgrade Do I need to add a wire going from the ALT to the battery positive terminal?