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  1. #1
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    Few questions about Sniper wiring

    Iím installing a Sniper efi on my Chevelle with a trunk mounted battery and AAW classic update kit. BBC with HEI. I have a few questions about the wiring,
    1. Main power wire, does it need to go all the way back to the trunk mounted battery or can I pull power from the AAW fuse panel or from a distribution block that I have near the starter which is connected directly to the battery? Can I ground to a clean chassis ground or does it have to go back to the battery?
    2. I already have a pre-run wire from the AAW for an electric fuel pump. Can I use this wire or do I need to use the fuel pump wire that comes in the Sniper harness?
    3. The yellow wire for rpm input, can I plug that in to the HEI if Iím already using the tach location on the HEI for a DD tach? Basically, can I piggy back the tach output and the efi rpm input from the same location on the HEI?
    4. Switched ignition wire, whatís the best location for this? Up to the ignition switch, or can this be pulled from the distributor? Other location?
    Thanks for any help!

  2. #2
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    1. Main power wire needs to go all the way back to the trunk mounted battery or pull power from a distribution block. Ground to the battery. All aftermarket FI like to go straight to the battery. Less issues that way.
    2. Use the fuel pump wire that comes out from the Sniper harness.
    3. The yellow wire for rpm input can piggy back from the same location on the HEI but I would use the tach output wire from the Sniper to feed the DD cluster.
    4. Switched ignition wire up to the ignition switch or from any switched ignition wire on the AAW harness. Definitely not from the coil.

    HTH

    Alex

  3. #3
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    Quote Originally Posted by CapSS92 View Post
    1. Main power wire needs to go all the way back to the trunk mounted battery or pull power from a distribution block. Ground to the battery. All aftermarket FI like to go straight to the battery. Less issues that way.
    2. Use the fuel pump wire that comes out from the Sniper harness.
    3. The yellow wire for rpm input can piggy back from the same location on the HEI but I would use the tach output wire from the Sniper to feed the DD cluster.
    4. Switched ignition wire up to the ignition switch or from any switched ignition wire on the AAW harness. Definitely not from the coil.

    HTH

    Alex
    Sound advice here....

    Don
    1969 Camaro - LSA 6L90E AME sub/IRS
    1957 Buick Caballero - huge project
    1959 El Camino - Ironworks frame
    1969 Mustang Sportsroof
    1956 Cameo - full C5 suspension/drivetrain

  4. #4
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    I'll expand a bit more here. The Sniper need CLEAN power straight from the battery and it's even better to use a dual post battery so the battery can buffer the "dirty power".

    ie: use the side post terminals only for the Sniper power leads and use the top post terminals for all other connections to the car.

    Regarding the fuel pump, use the pump wire from the Sniper to trigger a relay and use full power from that relay to power the fuel pump.

    In fact, use relays every where...like the 12v key on switch, have it trigger a relay and have that relay feed full 12v power to the Sniper.

    I'm not sure on the tach question but I'd be careful again about a "dirty" signal going into the Sniper ECU. If you follow the tech boards and forums on Sniper issues, almost 100% of those problems people have with their installs come back to shortcuts in wiring and dirty interference. Be super clean and diligent beforehand during the install and save yourself a ton of headaches later.
    Lance
    1985 Monte Carlo SS Street Car

  5. #5
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    Thanks guys, I appreciate the info. Time to get to work in it.

  6. #6
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    Quote Originally Posted by SSLance View Post
    I'll expand a bit more here. The Sniper need CLEAN power straight from the battery and it's even better to use a dual post battery so the battery can buffer the "dirty power".

    ie: use the side post terminals only for the Sniper power leads and use the top post terminals for all other connections to the car.

    Regarding the fuel pump, use the pump wire from the Sniper to trigger a relay and use full power from that relay to power the fuel pump.

    In fact, use relays every where...like the 12v key on switch, have it trigger a relay and have that relay feed full 12v power to the Sniper.

    I'm not sure on the tach question but I'd be careful again about a "dirty" signal going into the Sniper ECU. If you follow the tech boards and forums on Sniper issues, almost 100% of those problems people have with their installs come back to shortcuts in wiring and dirty interference. Be super clean and diligent beforehand during the install and save yourself a ton of headaches later.

    Holley is worried about transient voltage damaging your ECU. It's a CYA for warranty purposes IMHO...You can connect that ECU to pull power from anywhere and 99% of the time will run just fine. Nearly everything you buy for these older cars say to "connect directly to the battery". If your battery is in the trunk...that's alot of wires passing through the cabin. fuel/fan PWMs...Vintage Air...ECU...Radios etc..etc...where do you draw the line?

    I'm a rebel....All my stuff is connected on a junction block and a single large ga wire from the battery in the trunk to the firewall. Its been this way for YEARS! and no issues. Granted it might bite me one day...but I doubt it. How many modern cars do you think have all their electronic systems connected directly to the battery???

    I question Holley's product quality if they cant handle small variations of power fluctuation. I get it if the car gets struck by lightning...but come on even that and your stuff it toast anyway.

    1970 Camaro/DSE build


    Are you driver enough? Maybe....come on blue!
    https://www.pro-touring.com/threads/...71#post1147371


  7. #7
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    Quote Originally Posted by badazz81z28 View Post
    Holley is worried about transient voltage damaging your ECU. It's a CYA for warranty purposes IMHO...You can connect that ECU to pull power from anywhere and 99% of the time will run just fine. Nearly everything you buy for these older cars say to "connect directly to the battery". If your battery is in the trunk...that's alot of wires passing through the cabin. fuel/fan PWMs...Vintage Air...ECU...Radios etc..etc...where do you draw the line?

    I'm a rebel....All my stuff is connected on a junction block and a single large ga wire from the battery in the trunk to the firewall. Its been this way for YEARS! and no issues. Granted it might bite me one day...but I doubt it. How many modern cars do you think have all their electronic systems connected directly to the battery???

    I question Holley's product quality if they cant handle small variations of power fluctuation. I get it if the car gets struck by lightning...but come on even that and your stuff it toast anyway.
    Thanks, this is how I was hoping to wire it. I have a 00 cable that goes directly from the trunk mounted battery to the firewall where I could pull the power from. The car has a full interior in it, and I have hidden wiring throughout. So to get the wires to the trunk mounted battery, Iíd need to remove the center console which has a ton of wiring in it, then the kick panel, the carpet, the back seat, the trunk upholserty. That being said, I want to do it the right way, whichever way that is.

  8. #8
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    Quote Originally Posted by badazz81z28 View Post
    Holley is worried about transient voltage damaging your ECU. It's a CYA for warranty purposes IMHO...You can connect that ECU to pull power from anywhere and 99% of the time will run just fine. Nearly everything you buy for these older cars say to "connect directly to the battery". If your battery is in the trunk...that's alot of wires passing through the cabin. fuel/fan PWMs...Vintage Air...ECU...Radios etc..etc...where do you draw the line?

    I'm a rebel....All my stuff is connected on a junction block and a single large ga wire from the battery in the trunk to the firewall. Its been this way for YEARS! and no issues. Granted it might bite me one day...but I doubt it. How many modern cars do you think have all their electronic systems connected directly to the battery???

    I question Holley's product quality if they cant handle small variations of power fluctuation. I get it if the car gets struck by lightning...but come on even that and your stuff it toast anyway.
    Your approach is fine if the wire gauge is large enough imho. Skimp on that wire gauge and you could create problems. I would use battery cable. Thatís what the OEMs do.

    Of course that will ignite the whole trunk mounted solenoid debate.

    Don
    1969 Camaro - LSA 6L90E AME sub/IRS
    1957 Buick Caballero - huge project
    1959 El Camino - Ironworks frame
    1969 Mustang Sportsroof
    1956 Cameo - full C5 suspension/drivetrain

  9. #9
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    Quote Originally Posted by 65 drop top View Post
    Thanks, this is how I was hoping to wire it. I have a 00 cable that goes directly from the trunk mounted battery to the firewall where I could pull the power from. The car has a full interior in it, and I have hidden wiring throughout. So to get the wires to the trunk mounted battery, Iíd need to remove the center console which has a ton of wiring in it, then the kick panel, the carpet, the back seat, the trunk upholserty. That being said, I want to do it the right way, whichever way that is.
    That will be fine imho. I have done it that way on multiple builds. The issues arise when guys use 14 gauge wire etc.

    This is a controversial subject so you are going to get widely varying opinions.

    Don
    1969 Camaro - LSA 6L90E AME sub/IRS
    1957 Buick Caballero - huge project
    1959 El Camino - Ironworks frame
    1969 Mustang Sportsroof
    1956 Cameo - full C5 suspension/drivetrain

  10. #10
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    Quote Originally Posted by dhutton View Post
    That will be fine imho. I have done it that way on multiple builds. The issues arise when guys use 14 gauge wire etc.

    This is a controversial subject so you are going to get widely varying opinions.

    Don
    What do you think about the fuel pump wiring? I had run a wire from the AAW to the trunk when the car got wired. All Iíd need to do is pop the fuse in place and its ready to go. Or do I need to use the fuel pump wiring from the sniper harness? If I have to run the sniper fuel pump wire to the back then I may as well run the sniper main power wire back too. But if I pull the sniper power from the junction at the firewall, it would be nice if I could use the AAW fuel wire thats already run.

  11. #11
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    The Sniper needs to control the fuel pump as far as I know. Same as the GM ECM.

    Can’t you just splice the Holley fuel pump wire to the one you already ran to the trunk?

    Don
    1969 Camaro - LSA 6L90E AME sub/IRS
    1957 Buick Caballero - huge project
    1959 El Camino - Ironworks frame
    1969 Mustang Sportsroof
    1956 Cameo - full C5 suspension/drivetrain

  12. #12
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    I would still be concerned about dirty/noisey electrical wires running right with/parallel to clean power wires. If the power wire from your alternator is on the same circuit as the power wire to the Sniper, you are just asking for trouble. Heck, even if they are in separate rooms but zip tied together you are asking for trouble.

    I understand the issue of not wanting to disassemble the car...but if it wont run right after the install is done and is plagued with RFI, what are you going to do then?
    Lance
    1985 Monte Carlo SS Street Car

  13. #13
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    Quote Originally Posted by SSLance View Post
    I would still be concerned about dirty/noisey electrical wires running right with/parallel to clean power wires. If the power wire from your alternator is on the same circuit as the power wire to the Sniper, you are just asking for trouble. Heck, even if they are in separate rooms but zip tied together you are asking for trouble.

    I understand the issue of not wanting to disassemble the car...but if it wont run right after the install is done and is plagued with RFI, what are you going to do then?
    Hence the need to use a battery cable sized wire. Low impedance wire connected to a low impedance battery implies the end of the wire is essentially the same point as the battery itself. Issues arise when small gauge wire is used, giving a high impedance connection. Noisy currents flowing in a high impedance wire will generate noise for other circuits connected to that wire.

    Take a look at a newer Camaro with a trunk mounted battery. It is done exactly this way.

    When in doubt follow the lead of the OEMs.

    Don
    1969 Camaro - LSA 6L90E AME sub/IRS
    1957 Buick Caballero - huge project
    1959 El Camino - Ironworks frame
    1969 Mustang Sportsroof
    1956 Cameo - full C5 suspension/drivetrain

  14. #14
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    So this is what I'm getting at, and maybe I'm not understanding the OPs intentions completely.

    Say you run a 0 gauge wire from trunk mounted battery to distribution block on firewall (good right?) and then have your starter, alternator, coil, electric fans etc along with the Holley Sniper main power harness all connected to the distribution block for power. What is going to insulate the dirty noise from the starter, alternator, fans etc from the clean power the Sniper needs on the distribution block?

    Every video and tutorial Holey puts out about these systems stresses "garbage in, garbage out" and the important need to isolate completely the dirty power from the ECU. Why not follow their advice?
    Lance
    1985 Monte Carlo SS Street Car

  15. #15
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    I don't run the power wires directly back to the battery either, for the same reason you guys mentioned. In fact I think you would actually end up creating a dirty electrical environment because you would have all these long power wires running throughout the vehicle. Another thing to consider when wiring everything to the trunk battery is that the main source of power actually comes from the alternator's regulator when the engine is running and not the battery. So with a trunk battery you would have current flowing from the regulator back to the trunk battery and then back to the front of the vehicle, just think about all the noise that's going to create.

    The same goes for the ground wires, I always try to connect the ground wire to the car body with a short piece of wire. After all the car body is a better conductor than a wire running the length of the body and it won't emit as much noise either. Likewise I run a short ground wire from the trunk battery to the frame. What you want to avoid doing is sharing power wires from the distribution point with multiple components especially if those components are noise generators.

  16. #16
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    Quote Originally Posted by SSLance View Post
    So this is what I'm getting at, and maybe I'm not understanding the OPs intentions completely.

    Say you run a 0 gauge wire from trunk mounted battery to distribution block on firewall (good right?) and then have your starter, alternator, coil, electric fans etc along with the Holley Sniper main power harness all connected to the distribution block for power. What is going to insulate the dirty noise from the starter, alternator, fans etc from the clean power the Sniper needs on the distribution block?

    Every video and tutorial Holey puts out about these systems stresses "garbage in, garbage out" and the important need to isolate completely the dirty power from the ECU. Why not follow their advice?
    The low impedance connection to the battery will isolate it. The noise can’t be imparted onto the low impedance connection.

    Holley says not to do it because guys will use a wire that is too small gauge. Do they show the case of a trunk mounted battery? It’s a bit of a different case from a battery under the hood.

    Not trying to be a butthead but yes I do have a degree in electronics engineering and 35 years of hardware design experience. I believe the same applies to Blitzer454.

    Don
    1969 Camaro - LSA 6L90E AME sub/IRS
    1957 Buick Caballero - huge project
    1959 El Camino - Ironworks frame
    1969 Mustang Sportsroof
    1956 Cameo - full C5 suspension/drivetrain

  17. #17
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    Damn Don now I feel old, actually I only have 28 years of experience so you remain the old fart. I feel better now.

  18. #18
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    Quote Originally Posted by blitzer454 View Post
    Damn Don now I feel old, actually I only have 28 years of experience so you remain the old fart. I feel better now.
    Ya but I donít look a day over 40.

    Don
    1969 Camaro - LSA 6L90E AME sub/IRS
    1957 Buick Caballero - huge project
    1959 El Camino - Ironworks frame
    1969 Mustang Sportsroof
    1956 Cameo - full C5 suspension/drivetrain

  19. #19
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    Quote Originally Posted by dhutton View Post
    The low impedance connection to the battery will isolate it. The noise canít be imparted onto the low impedance connection.

    Holley says not to do it because guys will use a wire that is too small gauge. Do they show the case of a trunk mounted battery? Itís a bit of a different case from a battery under the hood.

    Not trying to be a butthead but yes I do have a degree in electronics engineering and 35 years of hardware design experience. I believe the same applies to Blitzer454.

    Don

    If the noise is hooked to the distribution block and the Sniper is hooked to the same distribution block, what will isolate those connections from each other? Aren't they hooked directly together by the distribution block?
    Lance
    1985 Monte Carlo SS Street Car

  20. #20
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    Lance, the low impedance connection to the battery makes this a low impedance node and as such the signal does not appear there. It is attenuated in the wire feeding the node since it has a higher impedance. It’s really no different than if the connections are made directly to the battery. The large diameter battery cable simply extends the battery post to the front of the car.

    Sorry I don’t know how to better explain this.

    There’s nothing wrong with the Holley approach other than it’s messy and can generate RFI as Blitzer stated. But the OP doesn’t want to rip his car apart to implement it.

    I’ve done it this way on several builds without issue. Key is to use a large size battery cable and not a small gauge wire.

    Don
    1969 Camaro - LSA 6L90E AME sub/IRS
    1957 Buick Caballero - huge project
    1959 El Camino - Ironworks frame
    1969 Mustang Sportsroof
    1956 Cameo - full C5 suspension/drivetrain

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