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Thread: Wiring considerations for Holley EFI systems.

  1. #1

    Default Wiring considerations for Holley EFI systems.

    I’ve had it in my mind for a while to make this post, but my experience last week has finally pushed me over the edge. This post is applicable to not just Holley Sniper EFI (or any EFI system) installations, but also applies to LS swaps into just about any older vehicle.

    Last week I had an opportunity to work on a 1968 Chevelle SS396. It was a very cool, mostly original car, with no rust and great patina, in butternut yellow. I was originally hired to simply tune the car, but it became very apparent that if this car was to be reliable (the car was to be driven often by an older gentleman), it needed to be completely rewired under the hood.

    This particular car already had a Holley Sniper EFI system installed and was running and driving. The decision was made to also upgrade the ignition system with a Holley HyperSpark ignition box and Sniper coil. A Holley distributor was already installed. However, the wiring under the hood was a complete mess. Wires were run haphazardly and there were plastic butt connectors everywhere. Numerous electronic components received their power from a post on the hot side of a ballast resistor that was attached to a bracket at the rear of the intake manifold. This post received its power from the original pink wire that came from the ignition switch.

    To make matters worse, there were two 12” Spal fans. These fans were not controlled by the Sniper, but used a Mishimoto fan controller that used a temperature probe that was inserted into the radiator. Looking up the Spal fan part number showed that each fan was rated at 35 amps, which is presumably the inrush current rating. Both fans were wired into the single fan controller that was clearly labeled to only be rated at 25 amps. There were no fuses for the fans, or for any other accessories that were being powered from the ballast resistor. As an additional bonus, the fans were powered from an insulated stud on the core support in front of the battery and the same post is where the power wire for the Sniper EFI was attached. When the fans kicked on, the car would stall. This was not a tuning issue, but was caused by a momentary voltage drop to the Sniper EFI.

    The Problem.
    Old cars had very simple engine electronics and do not have any functional power sources under the hood. When adding modern EFI, ignition, fans, and other accessories, an additional power distribution module must be added under the hood.

    The Solution. (My preferred vendor of choice is Waytek Wire.)
    There are many ways to solve this problem, but I'm going to present the one that I feel offers a balance of simplicity, functionality, and cost. Eaton’s Bussmann product line offers many power distribution modules that can be used to address the current problem. My personal favorite is this particular module: It's Bussmann part number 15305-2-2-4, Waytek part number 46343.

    What makes this panel uniquely suited for this application is the fact that the panel incorporates two built in buses. The first bus powers all of the fuses and can also be jumped to power the #30 terminal of the relays. The second bus powers the #86 terminal of the relays. The first bus gets connected to the positive side of the battery, while the second bus gets powered by a wire from the car’s existing ignition wire that is hot when both in the RUN and CRANK positions of the ignition key. With older GM cars, this will be the pink wire that originally provided power for the coil. As a side note, on my 1967 Cougar, this wire was also pink.

    This panel and all of the related components are sold individually, so care must be taken when ordering components. We must also understand the vocabulary that describes the various components. Terminals are the metal contacts that are crimped on the end of the wires and inserted into the panel. Cable seals are little silicone boots that slide on the wire before the terminals and get crimped by the terminal around the wire insulation to maintain water resistance. The Bussmann panel uses Metri-Pack 280 series terminals that are “tangles.” These are slightly different than those used in Metri-Pack 280 series connectors. Page number 178 of the Waytek catalog lists 4 different terminals that together accommodate whatever gauge wire is being used. There are also 4 different cable seals. The cable seals all have the exact same outer diameter, but have differing inside diameters to maintain a tight seal around the wire insulation. The last components that will be required are the green cavity plugs. These will be used to seal the cavities that are not being used after the panel is fully assembled, again, to maintain water resistance.

    Crimping tools for terminals can get very expensive. However, once you have used a proper set of crimpers, you'll never want to use anything else. For this particular project, the most cost effective option is the Sargent 3186CT crimper:

    It works with a variety of gauge wires and terminal sizes and has the capacity to crimp both the terminals and the cable seals. It will crimp wires gauges 20-14, and with a little care, will also crimp 12 gauge (this is the largest gauge wire that will be needed) terminals.

    Other things to consider are the various other terminals that might be needed. Using cheap, plastic butt connectors from the parts store is just asking for trouble. I prefer using un-insulated butt and ring terminals. Waytek carries an excellent selection of Molex butt connectors.

    They not only make terminals to mate same gauge wires together, but also transition butt terminals that allow the mating of different gauge wires to be connected together. I also use adhesive lined heat shrink, exclusively. This seals the butt joint and eliminated moisture from corroding the butt joint. This type of heat shrink is commonly called “marine grade.”

    When doing any Holley EFI system (Sniper, Terminator X, HP, Dominator, etc.) it makes wiring simple, because Holley uses Metri-Pack connectors for many of the plugs. For instance, on the Sniper system, there are two main connectors. There is a 7-cavity hybrid connector that uses a mix of Metri-Pack 150 and Metri-Pack 480 terminals. The 480 series terminals are used for the main power leads that get connected to the battery and the 150 series terminals are used for other functions. The Sniper also has a 10-cavity 150 series connector that has wires for various purposes. On the Terminator X and other Holley systems there is an 8-cavity 150 series connector that serves as the Input/Output connector.

    I will outline what I did on the 1968 Chevelle, but the basics can be applied to most other vehicles. The first order of business is to physically locate all of the components that will need to be wired. The Sniper system has the ECU that is housed within the throttle body and has molded cables that have the 7-cavity and the 10-cavity connectors mentioned previously (both are male on the Sniper side). Those connectors were routed straight back and located against the firewall, along where the factory wire gutter is bolted to the firewall. The Sniper coil was located on the driver’s side wheel well. The HyperSpark box located on the passenger side wheel well and the Bussmann panel was located just in front of it, which puts it optimally close to the battery.

    The Sniper harness includes a fuel pump relay (other Holley systems do not), so the decision was made to eliminate that relay and added it to the Bussmann panel for sake of simplicity. Holley has very strict instructions to wire the main power leads for the Sniper and the HyperSpark directly to the battery. For this reason, I prefer to use batteries with both top and side terminals. The top terminals serve their main purpose of providing the main vehicle ground and power directly to the starter (or in the case of older Fords, to the starter solenoid). There are adapters that are bolted into the side terminals and have a 3/8” stud where the Sniper and the HyperSpark are connected.

    The Sniper, HyperSpark and the distributor also have pink wires that serve as “turn on” signals. These do not carry significant current, but they must be powered when the ignition key is both in the RUN and CRANK positions (this is critical). This is where the original pink coil wire from the Chevelle’s existing wiring comes in. This wire gets routed to the #2 bus on the Bussmann panel. As stated before, this bus sends power to the #86 terminal (positive side of the relay coil) of all the relays. Remember, the #1 bus feeds one side of all the fuse terminals. So a small 12-gauge jumper is made to bridge the other side of the fuse and the #30 terminal (switched power input on the relay) under the Bussmann panel. This brings power directly from the battery, through a fuse, to the relay. Lastly, all of the pink wires from the Sniper, HyperSpark and distributor are routed to the #87 relay cavity on the Bussmann panel. The #85 cavity is grounded. So, as soon as the ignition switch is put in the RUN position, the Sniper, HyperSpark, and the distributor receive their “turn on” signal and they will remain ON as the engine is cranked.

    As stated earlier, the decision was made to add the fuel pump relay to the Bussmann panel. The basic procedure is followed here with a small exception. Again, a jumper is made from the open side of a fuse cavity to the #30 terminal of the fuel pump relay. The #86 terminal already has power from the #2 bus. The exception here is that the #85 terminal is wired to the light blue wire that comes out of the 7-cavity connector on the Sniper harness. This sends a ground signal to the fuel pump relay coil, and thus turns on (or off) the fuel pump as directed by the Sniper EFI. The #87 wire is routed back to the fuel pump.

    The Sniper has two available cooling fans outputs. These were wired almost exactly as the fuel pump. One relay is used for each fan. Jumpers are made from the open side of the fuse to the #30 terminals of the relays. The #86 terminal is already powered, and the #85 terminals are wired to the fan #1 and fan #2 outputs from the Sniper ECU (these are located on the 10-cavity plug). The #87 terminals of the relays are routed to the fans. The ground side of the fan motors are connected directly to the side terminals of the battery.

    Lastly, whenever possible butt splices were avoided. I ran new wires whenever needed. For instance, the fuel pump and both of the fan trigger wires needed to be extended. I used new lengths of 20-gauge wire that connected the connectors on the Sniper harness and were routed to the Bussmann panel. As mentioned before, this is easily done by purchasing female Metri-Pack 150 series terminals and properly installing them into the Sniper connectors. This was also done for the main power leads to the Sniper (these use female Metri-Pack 480 terminals). The crimping tool that I mention earlier will do all of these terminations.

    As I said earlier, there are many ways to do this properly, this is just my way. If there are any questions or comments, please post them up.
    IG @projectgattago
    I offer remote Holley EFI tuning.
    I deliver what EFI promises.
    Please get in touch if I can be of service.

  2. #2


    I'm trying to post pictures, but they all seem to be automatically rotated for some reason. They're definitely in the proper orientation, but the forum software is rotating them 90 degrees, so I'll post them as links instead of embedded. Andrew

    Here's the Chevelle:

    This is the 7-cavity hybrid Metro-Pack connector that's on the Sniper. You can see the two large gauge power wires (480) and the 5 small wires (150):

    Here are the HyperSpark and the Bussmann panel mounted on the driver's side:

    I retained the inline fuse that is part of the Holley power harness, so that the power feeds go directly to the battery:

    Here you can see the little red loops that I mentioned. These are the jumpers from the open side of the fuses to the #30 terminals of the relays. The pink wire with the ring terminal is the original pink wire from the ignition switch with the marine heat shrink over it. The blue, pink, red, and green are for fuel pump, turn-on for the Sniper, and fans 1 and 2, respectively:

    This just shows the wire path going from the panel to the Sniper plugs, which are near the firewall:

    I also added to separate relays in order to be able to utilize the A/C Kick and A/C Shutdown functions in the Sniper. The A/C Kick also turns on Fan #1. I couldn't use the Bussmann panel for these because of how the relays had to be wired and one of the relays needed to use the 87A terminal. I like using these Delphi relay holders which are water resistant when used with skirted relays:

    The relay holder uses Metro-Pack 630 series pull to seat terminals:

    Everything was loomed with nylon split loom and the branches were taped with 3M cotton friction tape:

    Lastly, I made a secret decoder, so that future troubleshooting will be a lot easier:

    Last edited by andrewb70; 07-16-2020 at 01:38 PM.
    IG @projectgattago
    I offer remote Holley EFI tuning.
    I deliver what EFI promises.
    Please get in touch if I can be of service.

  3. #3


    Here's a shopping list I put together for a friend who is about to wire a Holley Terminator X system into his LSx swapped second generation Trans Am. Andrew
    IG @projectgattago
    I offer remote Holley EFI tuning.
    I deliver what EFI promises.
    Please get in touch if I can be of service.

  4. #4


    @andrewb70: Are your relays installed upside down or right-side up? I've seen other tutorials that install upside down, but could not tell from your pictures. Do you have a ground wire coming out to an external bus or some other location from each #85 terminal? Can you explain your fuse layout and size? Looks like there are three in a row at the top in different sizes, and two 30 amp for the fans? I'm in the process of wiring my truck up and using your tutorial for reference. It's very good and detailed.

  5. #5


    The relays are installed right-side up. The 85 terminals are wired as needed. For instance, relays number 1, 3 & 4 have #85 terminals grounded by the ECU. Those are the fuel pump and the two fan relays. Relay number two has the #85 pin grounded to the chassis, so it's activated as soon as the ignition key is turned on.

    The rating for the fuses are estimated given the current draw of the device. For instance, the fans that were used on the Chevelle I believe were rated at about 20 amps continuous. However, at startup, they pull more current for a split second. Fuses are really meant to protect the wires in the event of a short or device malfunction that results in a short. We want the fuse to blow before the wire gets hot, melts, and catches fire. Andrew
    IG @projectgattago
    I offer remote Holley EFI tuning.
    I deliver what EFI promises.
    Please get in touch if I can be of service.

  6. #6


    Thanks, that explains it for me. I'm looking forward to finishing my wiring and seeing how it works. Thanks again.

  7. #7


    Glad to help. I was beginning to wonder if people were just thinking I was crazy for posting all that information...LOL. Andrew
    IG @projectgattago
    I offer remote Holley EFI tuning.
    I deliver what EFI promises.
    Please get in touch if I can be of service.

  8. #8
    Join Date
    Dec 2009


    Andrew, this is a great, very informative thread. Thanks for your time 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, Dominator MPFI & DIS, 36-1 crank trigger/1x cam sync, 200A 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, -6AN fuel system plumbing, Walbro 255 LPH pump, S&W subframe connectors, LenTech Strip Terminator wide-ratio AOD/3000 RPM converter, B&M Hammer shifter, 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.

  9. #9


    Thanks Danny. I think if everyone followed these guidelines people would have much more reliable EFI system installations and a lot less issues. Andrew

  10. #10


    Very Nice writeup!
    I've fixed quite a few vehicles that were a wiring nightmare. Got two waiting to come to the shop next week that are a mess. 16 AWG speaker wire feeding two Walbro 255 fuel pumps on one car. The wires are twisted together at the fuel pumps with tape over them. Truck I just finished had 20 AWG wire run to the fuel pump and a melted 16 AWG wire running two Electric fans.

    I like how the Eaton box hides all the wires underneath it. I use the Blue Sea Systems #5026 on most builds. But I'll have to try some of those Eatons.

    Thanks for taking the time to share all that!

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