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Thread: Keyed Power/Relay Question

  1. #1

    Default Keyed Power/Relay Question

    Hi everyone. I have a Sniper with a Dual Sync distributor and a 6A MSD box. The Sniper and Dual Sync distributor pink wires need keyed power. The MSD box has the small red wire that also needs keyed power. I'd like to use a four pole relay to decrease the chance of RFI. Do I need to use one relay per wire, or can I connect all three together and use one relay? Thanks, Geoff

  2. #2

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    I power all three on my setup through one relay and haven't had any issues. The fused supply for the relay runs straight to the battery.

  3. #3
    Join Date
    Oct 2020
    Location
    Ontario, Canada
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    158

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    You need to ensure that the relay trigger wire from the keyed switch is powered at both Run and Start positions. Generally, the original coil positive-side wire (or power wire to an electronic ignition module) is OK. Some older vehicles fed the coil from a separate "pigtail" on the solenoid during starting, so there isn't a continuous ignition supply from the keyed switch. The change from Start to Run will then cause a power interruption to that relay. The ECU will probably reset from this.

  4. #4

    Default

    Excellent, thank you both. I'll confirm keyed power. I'd like to locate the relay near the fuel pump relay. Is there any harm in splicing into the fused power going to the fuel pump relay in order to power the #30 post of the new relay? I believe the amperage pull from these three trigger wires will be low, and the power out from the relay would be clean. Thanks, Geoff
    Last edited by Geoff H; 11-23-2021 at 04:45 PM.

  5. #5
    Join Date
    Dec 2009
    Location
    Connecticut
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    29,437

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    Yes, ensure the Switched +12V pink wire (Sniper EFI) is powered in the "Run" and "Crank" key positions.
    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, 100HP progressive dry direct-port NOS, R134a A/C, 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 in-tank pump & Pro-M -6AN hanger, 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.

  6. #6

    Default

    Thanks Danny! I confirmed switched +12V power tonight. I can use that to fire the relay. For the power source going to the relay #30 pole, is it OK to use the same power source that's going to the fuel pump relay? I want to mount them in the same area so it'd simplify my wiring choice. Thanks, Geoff

  7. #7
    Join Date
    Dec 2009
    Location
    Connecticut
    Posts
    29,437

    Default

    That should be fine. See post #2 from GPatrick above.
    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, 100HP progressive dry direct-port NOS, R134a A/C, 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 in-tank pump & Pro-M -6AN hanger, 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.

  8. #8

    Default

    Perfect, thanks again!

  9. #9

    Default

    I highly recommend the use of a relay to generate the "pink" wire signal (hot in run/crank). Mechanical ignition switches have brass contacts that slide between the run & start position. This mechanical motion can create something known as "contact bounce". A carbureted system will never notice this. But it may cause the Sniper ECU to reset from time to time during starts. The relay acts as a "low pass filter" to prevent the contact bounce from being seen by the Sniper. Older ignition switches can really be prone to this. In my installation, I used a Mercedes OVP relay which not only suppresses this, but also suppresses EMI related voltage spikes.

  10. #10

    Default

    Interesting, could very well be what was happening in my situation.

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