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Thread: Separate fuses & relays for ECU and fuel pump.

  1. #1

    Default Separate fuses & relays for ECU and fuel pump.

    Hi. Holley HP EFI wiring an unterminated harness. I'd like to run separate fuses & relays for the ECU and fuel pump from the +12V input. This is not the power harness. What should the fuse rating be for just the ECU? Thanks, Don

  2. #2


    The ECU gets power on a dedicated harness that goes to the battery and that harness already has a fuse. You need to be a little more specific as to which loose wire you're referring to. Andrew

  3. #3
    Join Date
    Dec 2009


    The Holley 558-308 ECU Main Power Harness has a 40 amp fuse on it.
    May God's grace bless you in the Lord Jesus Christ.
    '92 Ford Mustang GT: 385" SBF, Dart SHP 8.2 block, TFS T/W 11R 205 heads, 232°-244° duration/.623" lift/114° LSA camshaft, 12:1 C/R, TFS R-Series FTI ported intake, BBK 80mm T/B, Holley Dominator MPFI & DIS, 36-1 crank trigger, 1x cam sync, 200A 3G alternator, Optima Red battery, R134a A/C, 100HP progressive dry direct-port NOS, Spal dual 12" fans, Frostbite 3-core aluminum radiator, Pypes dual 2.5" exhaust, off-road X-pipe, shorty headers, -6AN fuel system plumbing, Walbro 255 LPH pump, S&W subframe connectors, BMR upper & lower torque box reinforcements, LenTech Strip Terminator wide-ratio AOD, 3000 RPM converter, B&M Hammer shifter, Stifflers trans crossmember & driveshaft safety loop, FPP aluminum driveshaft, FPP 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 M/T Street Comp tires.

  4. #4


    @Donski: There's no reason why you can't put the injectors and the coils on separate relays. I'm currently installing a Terminator X on my own project and plan to do just that. Andrew
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  5. #5
    Join Date
    Nov 2014
    Ont. Canada


    I used a Unterminated 15' Flying Lead Main Harness and moved everything to the trunk.
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  6. #6


    Sorry for all of the confusion. I posted earlier that I made a mistake, but I guess it didn't post. I have the main harness with the 40A fuse. My original question was about the 14 AWG red wire that feeds the fuel pump relay and has a 30A fuse. I see now that it doesn't power the ECU, but instead powers the fuel injector harness as well as the fuel pump. I thought originally I'd want to split the relay, but it now makes perfect sense to have the fuel pump and injectors on the same relay. Danny, you can delete this post if possible. It's probably too confusing or misleading. Thanks.

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