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Thread: HP/Holley Dual Sync/MSD 6AL-2 Combo Wiring Diagram?

  1. #1

    Default HP/Holley Dual Sync/MSD 6AL-2 Combo Wiring Diagram?

    On my 'scratch-build' (no OEM stuff) E85 powered, N/A big block Ford street rod with the Holley HP ECU (554-113), I'm using the Holley 558-508 main harness, Holley 565-210 Dual Sync distributor, and sensor numbers 554-101, 534-20, 534-10, 554-102, 554-103. Also using MSD 6421 6AL-2 & MSD 8253 HVC-2 coil. I've looked through all the available diagrams and can't determine which would be closest to my combination. Could someone help me out with that? Both I & my engine builder have limited experience with Holley EFI.

  2. #2


    Schematic 271R960A-1 is what matches the 558-508 harness. The basic wiring is all the same, and pretty easy, since you already have a dual sync distributor.
    Click image for larger version. 

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  3. #3
    Join Date
    Dec 2009


    Originally Posted by Danny Cabral
    FYI: Holley EFI now sells their own Dual Sync Hall-Effect distributors (LINK).
    They're a small cap design, "plug & play" with Holley EFI, and no need for a modified Firing Order.
    The crank & cam sensor signals also provide sequential injection capability (MPFI applications).
    It's "plug & play" (into the 10-pin ignition connector on the EFI Main Harness) and requires a CD
    ignition box (Instructions). The MSD 6201 Digital 6A CDI box & 8253 HVC-2 coil are a great match.
    The MSD CD ignition box is wired as shown in the Holley EFI Wiring Manual: (Holley EFI Wiring Manual - Figure 11, Page 20) (Holley EFI Dual Sync Distributor - YouTube Tech Video)
    A blank cap (LINK) is available, if the user decides to convert to Coil-Near-Plug/DIS later (no CDI box).
    Of course, this component can also be used as a crank and/or cam sync/oil pump drive unit.

    The Custom Ignition Parameters (in System Parameters) for the Holley EFI Dual Sync Distributor:
    Ignition Type ............. ― "Custom"
    Crank Sensor Type ..... ― "1 Pulse/Fire"
    Sensor Type .............. ― "Digital Falling"
    Inductive Delay .......... ― "100.0 usec" ( Synchronization info, adjusted per application.)
    Ignition Reference Angle ― "50°" ( Inherent rotor-phasing of this unit.)
    Cam Sensor Type ........ ― "Single Pulse" ( "Not Used" for TBI, unless CNP ignition.)
    Sensor Type .............. ― "Digital Falling"
    Output Setup Type ..... ― "Points Output" ( CDI box ground trigger.)
    Dwell Time ................. ― "2.0 msec" ( Do not set this to 1.5 msec!)
    EFI Software Help Information/Instructions:
    ‒ On the top Toolbar, click "Help" & "Contents". This opens all Help topics.
    ‒ When navigating the software, click "Help ?", drag it to any parameter and click again.
    ..This automatically opens the definitions for that specific parameter.
    ‒ Tuning information can be read by clicking the F1 key, when you're viewing any screen. (Holley EFI Help/Instructions Overview) (Holley EFI Quick Start Guide) (Holley EFI Wiring Manual & Diagrams)! (Initial Checks & Adjustments - Read Steps #1-#6!)
    Open the Holley EFI software "Help" Contents ("Help" drop down menu), and read "Step-By-Step Beginners Tuning".
    Ensure the EFI software is set to run as an "Administrator" (right click for Properties/Advanced). Set it and forget it.
    May God's grace bless you in the Lord Jesus Christ.
    '92 Ford Mustang GT: 385" SBF, Dart SHP 8.2 block, TFS TW 11R 205 heads, 11.8:1 comp, TFS R-Series intake, Dominator MPFI & DIS, 36-1 crank trigger/1x cam sync, 160A 3G alternator, Optima Red battery, A/C, 100HP progressive dry direct-port NOS, Spal dual 12" fans/3-core Frostbite aluminum radiator, Pypes dual 2.5" exhaust/off-road X-pipe/shorty headers, S&W subframe connectors, LenTech Strip Terminator wide-ratio AOD/2800 RPM converter, M4602G aluminum driveshaft, 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.

  4. #4


    Thanks Fastman, I appreciate that! I worked with OEM EFIs for many years, but this is my first 'DIY' system.

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