Alt upgrade. Do I need to add a wire going from the ALT to the battery positive?
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This is a discussion on Alt upgrade. Do I need to add a wire going from the ALT to the battery positive? within the Engine Modifications forums, part of the Tech & Modifying & General Repairs category; I'm upgrading from a 75amp (PN: 23700-AA430) alternator to a 110amp (PN: 23700-AA570) alternator. Do I need to add a ...

  1. #1
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    Alt upgrade. Do I need to add a wire going from the ALT to the battery positive?

    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.

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  3. #2
    Registered User nsibanez's Avatar
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    your lights will dim every time your bass hits if the amp is kcking high enough power regardless of the alternator size. of course its going to say low output because its drawing a lot fo power from it to power your subs.
    do you have a capacitator installed/installed in the right place in the circuit? if not, that's probably the problem. if theres one installed already, the higher output alternator may help and you should get a thicker gauge wire to handle the extra current just incase

  4. #3
    Subaru Newb MainFrame's Avatar
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    For that slight of an upgrade I wouldn't think a bigger power wire is necessary. I doubled up on my alt-battery hot wire when I upgraded mine (160amp). It's certainly not going to hurt, and while you're at it I would do the "big three" as well as a little grounding mod for the engine sensors.

  5. #4
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    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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