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Thread: 558-307/556-128 install relay questions.

  1. #1

    Default 558-307/556-128 install relay questions.

    I think I have this correct, but just want to double check to make sure. Need two relays, fused power (20 amps each) to feed each side of 558-307 relay. One each side. And need one relay fused 40 amps to feed both sides of the harnesses in the 556-128 kit. All three are keyed on power. Thank you.

  2. #2
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    May God's grace bless you in the Lord Jesus Christ.
    '92 Ford Mustang GT: Dominator MPFI & DIS, A/C, Spal dual 12" fans/3-core Frostbite aluminum radiator, Pypes dual 2.5" exhaust/X-pipe/shorty headers, 100HP progressive dry direct-port NOS, 160A 3G alternator, Optima Red battery, LenTech Strip Terminator wide-ratio AOD/2800 RPM converter, FRPP 3.31 gears, Cobra Trac-Lok differential, Moser 31 spline axles, '04 Cobra 4-disc brakes, '93 Cobra booster & M/C, 5-lug Bullitt wheels & 245/45R17 tires.

  3. #3

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    There is another relay that can be considered as well with weather pack connectors: https://www.te.com/usa-en/product-14...-docs-features. The 558-307 universal harness asks for switched power capable of 20 amps to each side of that harness. Then the 556-128 asks for either a 40 amp or 75 amp relay depending on dwell. To power both sides of harness. Just trying to clarify. The link is saying all switched power can come off one relay?

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    Quote Originally Posted by 421stroker View Post
    There's another relay that can be considered as well with weather pack connectors: https://www.te.com/usa-en/product-14...-docs-features.
    Yeah, that's basically the same relay I linked, except it has a higher amperage rating of 130A.

    The 558-307 universal harness asks for switched power capable of 20 amps to each side of that harness. Then the 556-128 asks for either a 40 amp or 75 amp relay depending on dwell, to power both sides of harness. Just trying to clarify.
    If using the Holley 558-318 CNP coil sub-harness, then you don't use the "Relay +12V" red wire from the Holley 558-307 CNP main harness (that's for the GM LSx CNP sub-harnesses).
    Connect the two harnesses together and you'll see what I mean; it isn't even routed through the connectors into the Holley 558-318 CNP coil sub-harness. It's routed through on LSx coil sub-harnesses.

    The link is saying all switched power can come off one relay?
    Yes, if you're using the single 75 or 130 amp power relay. When using the Holley 558-318 CNP coil sub-harness, you only use its three loose unterminated wires, not the ones from the Holley 558-307 universal harness.
    May God's grace bless you in the Lord Jesus Christ.
    '92 Ford Mustang GT: Dominator MPFI & DIS, A/C, Spal dual 12" fans/3-core Frostbite aluminum radiator, Pypes dual 2.5" exhaust/X-pipe/shorty headers, 100HP progressive dry direct-port NOS, 160A 3G alternator, Optima Red battery, LenTech Strip Terminator wide-ratio AOD/2800 RPM converter, FRPP 3.31 gears, Cobra Trac-Lok differential, Moser 31 spline axles, '04 Cobra 4-disc brakes, '93 Cobra booster & M/C, 5-lug Bullitt wheels & 245/45R17 tires.

  5. #5

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    Yes, either/or is a very nice relay setup. I just got both boxes in and was reading the instructions separate. Thank you Danny for clarifying. Take care.

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    Quote Originally Posted by 421stroker View Post
    Thank you Danny for clarifying. Take care.
    You're welcome.
    May God's grace bless you in the Lord Jesus Christ.
    '92 Ford Mustang GT: Dominator MPFI & DIS, A/C, Spal dual 12" fans/3-core Frostbite aluminum radiator, Pypes dual 2.5" exhaust/X-pipe/shorty headers, 100HP progressive dry direct-port NOS, 160A 3G alternator, Optima Red battery, LenTech Strip Terminator wide-ratio AOD/2800 RPM converter, FRPP 3.31 gears, Cobra Trac-Lok differential, Moser 31 spline axles, '04 Cobra 4-disc brakes, '93 Cobra booster & M/C, 5-lug Bullitt wheels & 245/45R17 tires.

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