Switched 12v source

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ScampChamp

ScampChamp

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Hi guys I am installing a Holley sniper efi with Holley hyperspark ignition system on my 1975 Plymouth scamp with a 360. Holley says I need to hook up a certain wire to a switched 12v source (hot with key in ON position, and hot while cranking) and I cannot use the positive of the ignition coil they claim. I am really having trouble finding or figuring out where to go. I’m no electrician by any means. Any and all help will be greatly appreciated. Thanks so much

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yes stock wiring harness. And ballast resistor is already gone. (Currently running a MSD RTR dizzy
 
I put a Fitech on mine and the directions made the same claim, i think they need pretty clean power, i ended up putting in a relay run off the acc from the key.
 
There will be switched circuits on the fusebox... you may even find an unused terminal that you can tap right into. Use a meter or test light to find a circuit that goes on and off with the key. For example, the radio circuit.
 
toolmanmike said:
And run it through a relay.
Click to expand...

Right. Just come straight off the back of the ignition switch and to a dedicated relay. It is was me, and it will be in the near future, I would come off the ignition switch and go to a "positive buss" under the hood. That way, you can add other circuits later if need be. You'll want to fuse those circuits, though. If you add more in the future, you'll want to use a relay again, because that will take the full load off the ignition switch.
 
that should only be the trigger wire, not it's actual supply. On my Fitech, I just used the wire for the electric choke.. The power supply wire should be the one that runs direct to battery..
 
OK PLEASE LISTEN UP!!!

THERE IS NO switched 12V source that is hot both in "run" and in cranking!!! NONE!!! NADA!!! DOES NOT EXIST

So what?? do you do?

One thing you can do is get rid of your ignition system that DOES need a ballast resistor (if you still have it) and tie the ign1 and ign2 lines together coming out of the ignition switch

IGN1: This is the ONLY source of power under the hood or coming from the ignition switch that is "hot" in the "run" position. IT IS NOT HOT DURING CRANKING!!!

This is what comes from the ign switch, through the bulkhead, and feeds the ballast, the VR IGN terminal, and the alternator field in 70/ later cars, and some smog doo dads on some. Electric choke if you have one, idle stop solenoid if equipped, etc

IGN2: This is the ONLY source of ignition power during CRANKING It originally was the brown going to the coil+ side of the ballast, and therefore bypassed the ballast during cranking and also provided ignition power during this function

So, if you use an ignition system such as MSD, or integral in the EFI, or some other ignition (HEI) which does NOT use a ballast, you can connect those two sources together.

OTHERWISE you will have to use some diodes and a relay to provide a connection without disabling the function of the two. (Steering diodes)
 
67Dart273 said:
OK PLEASE LISTEN UP!!!

THERE IS NO switched 12V source that is hot both in "run" and in cranking!!! NONE!!! NADA!!! DOES NOT EXIST

So what?? do you do?

One thing you can do is get rid of your ignition system that DOES need a ballast resistor (if you still have it) and tie the ign1 and ign2 lines together coming out of the ignition switch

IGN1: This is the ONLY source of power under the hood or coming from the ignition switch that is "hot" in the "run" position. IT IS NOT HOT DURING CRANKING!!!

This is what comes from the ign switch, through the bulkhead, and feeds the ballast, the VR IGN terminal, and the alternator field in 70/ later cars, and some smog doo dads on some. Electric choke if you have one, idle stop solenoid if equipped, etc

IGN2: This is the ONLY source of ignition power during CRANKING It originally was the brown going to the coil+ side of the ballast, and therefore bypassed the ballast during cranking and also provided ignition power during this function

So, if you use an ignition system such as MSD, or integral in the EFI, or some other ignition (HEI) which does NOT use a ballast, you can connect those two sources together.

OTHERWISE you will have to use some diodes and a relay to provide a connection without disabling the function of the two. (Steering diodes)
Click to expand...
Thanks everybody for the responses and thank you 67dart. So I understand what you are saying about having to use both connected together. Sorry to sound really stupid but how do I go about “connecting them together? “ add 2 extra wires coming off the switch and into my wire from the efi kit? Or is that not even close. Thanks again so much
 
You have to understand what I posted. What do you have for an ignition system, that is, does the system you have USE A BALLAST resistor?

This is important, because you can NOT simply hook the two together with such a system.

If your ignition uses a ballast, you are going to have to use the relay/ diodes mentioned,

............If not......they can be bridged.

You don't have to dig clear back to the switch, you can get at them in the engine bay. Go download a service manual for your vehicle or as close as you can get from MyMopar

What year/ model do you have?

Also if you have a "mostly factory" wiring harness, the BULKHEAD CONNECTOR has it's own set of problems, and when adding such a system as this EFI you really SHOULD use a relay to power the ignition loads under the hood.

So first here's what we need to know?

1....What year model is your vehicle
2....What are you gonna use for an igntiion system?
3....Is the harness factory stock, or been aftermarket re-wired?
4....Also, detail "what else" you are gonna add.......electric fans? "Big" electric fuel pump? Electric water pump? Etc?
 
ScampChamp said:
yes stock wiring harness. And ballast resistor is already gone. (Currently running a MSD RTR dizzy
Click to expand...

LOL Somehow I missed this. You are likely already set up OK. The same wire that is now feeding your MSD "trigger wire" (small red? red/ white?) is what goes to the small trigger wire for the EFI

Before you finalize wiring, tho, you need to see if voltage drop is a problem. If it is runnable now, get it warm and read battery charging voltalge at a "medium cruise" RPM. IF it is charging at much over 14V say, 14.5 or more, then you have a voltage drop problem in the harness
 
67Dart273 said:
You have to understand what I posted. What do you have for an ignition system, that is, does the system you have USE A BALLAST resistor?

This is important, because you can NOT simply hook the two together with such a system.

If your ignition uses a ballast, you are going to have to use the relay/ diodes mentioned,

............If not......they can be bridged.

You don't have to dig clear back to the switch, you can get at them in the engine bay. Go download a service manual for your vehicle or as close as you can get from MyMopar

What year/ model do you have?

Also if you have a "mostly factory" wiring harness, the BULKHEAD CONNECTOR has it's own set of problems, and when adding such a system as this EFI you really SHOULD use a relay to power the ignition loads under the hood.

So first here's what we need to know?

1....What year model is your vehicle
2....What are you gonna use for an igntiion system?
3....Is the harness factory stock, or been aftermarket re-wired?
4....Also, detail "what else" you are gonna add.......electric fans? "Big" electric fuel pump? Electric water pump? Etc?
Click to expand...
Great thanks it is a #1 1975 Plymouth Scamp. #2 Holley hyperspark dizzy,coil, and box (no ballast resistor. #3 harness is stock. #4 will be running a high flow fuel pump and possibly electric fans one day. Thanks I have a manual with the diagrams I just wasn’t sure how to read and understand what I’m doing

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How about a hidden toggle switch fused to the battery. Also used as an ignition disable switch for theft. I’m running an FITech set up almost the same and gutted my ballets resistor and ran a straight 12ga wire behind it. But for the constant power I ran a toggle switch hidden for the straight battery power.
Works great!
 
I have a red, orange, and black coming from my distributor. The black goes to ground. And the red goes to coil + and the orange goes to coil - There is also a brown wire on the coil +. I am told in the efi kit. I cannot hook any wires to my coil except for the 2 wire that tell me too
 
Syleng1 said:
How about a hidden toggle switch fused to the battery. Also used as an ignition disable switch for theft. I’m running an FITech set up almost the same and gutted my ballets resistor and ran a straight 12ga wire behind it. But for the constant power I ran a toggle switch hidden for the straight battery power.
Works great!
Click to expand...

This is where I ended up. The issue I had was even with ign 1 and 2 tied together, the Sniper would reboot going from start to run. The momentary loss of power between the contacts in the switch caused it.
 
Gents, the Sniper and FiTech, require a constant 12v to drive everything, fans, fuel pump, ECU/ECU memory, etc. This should be 12v power coming directly from(and buffered by) the battery. They also both require a KEYED 12v source. This is simply a trigger wire for the internal relays. You want the power as clean as possible to prevent any interference(RPM Noise).
 
I have moved to a full American Autowire retrofit harness, so I am not certain on your stock '75 harness, but I suggest looking at the electric choke wire, and the excite wire for the alternator..
 
JoeSBP said:
I have moved to a full American Autowire retrofit harness, so I am not certain on your stock '75 harness, but I suggest looking at the electric choke wire, and the excite wire for the alternator..
Click to expand...

None of this is applicable, please re-read my post. There are only two lines off the ignition switch (actually three

They are:

ACCessory: Goes cold during cranking and of course hot in both "run" and "accessory"

"IGNITION RUN" or IGN1 This is the ONE wire which supplies such items as ignition, VR IGN terminal (power and sense) and alternator field. It supples electric choke if used, and other smog doo dads. IT IS NOT POWERED during "start" (cranking)

"Bypass" or IGN2 This wire only goes one place........from the ignition switch IGN2 terminal to the coil+ side of the ballast. It is hot ONLY in starting

To repeat the ONLY way to get power BOTH in "run" and in "start" is to either wire the above two together........or use isolation/ steering diodes to operate a relay

You can talk all you want but the "headwaters"---the source---is the ignition switch.
 
RustyRatRod said:
Right. Just come straight off the back of the ignition switch and to a dedicated relay. It is was me, and it will be in the near future, I would come off the ignition switch and go to a "positive buss" under the hood. That way, you can add other circuits later if need be. You'll want to fuse those circuits, though. If you add more in the future, you'll want to use a relay again, because that will take the full load off the ignition switch.
Click to expand...
You planning on buying a sniper from your favorite crate engine supplier:) ?
 
Last edited:
67Dart273 said:
None of this is applicable, please re-read my post. There are only two lines off the ignition switch (actually three

They are:

ACCessory: Goes cold during cranking and of course hot in both "run" and "accessory"

"IGNITION RUN" or IGN1 This is the ONE wire which supplies such items as ignition, VR IGN terminal (power and sense) and alternator field. It supples electric choke if used, and other smog doo dads. IT IS NOT POWERED during "start" (cranking)

"Bypass" or IGN2 This wire only goes one place........from the ignition switch IGN2 terminal to the coil+ side of the ballast. It is hot ONLY in starting

To repeat the ONLY way to get power BOTH in "run" and in "start" is to either wire the above two together........or use isolation/ steering diodes to operate a relay

You can talk all you want but the "headwaters"---the source---is the ignition switch.
Click to expand...

This is all applicable, because it is already established that you wire IGN1 and IGN2 two together together.
 
JoeSBP said:
This is all applicable, because it is already established that you wire IGN1 and IGN2 two together together.
Click to expand...

Then you are arguing the choir. You can NOT tie them together except if you get rid of the factory ignition system. When people make statements like "just tie it to the choke wire" this has to be established. Maybe I should have added "if", "unless"
 
67Dart273 said:
Then you are arguing the choir. You can NOT tie them together except if you get rid of the factory ignition system. When people make statements like "just tie it to the choke wire" this has to be established. Maybe I should have added "if", "unless"
Click to expand...

The OP already stated he is using a RTR distributor, so the factory ignition system is gone
On a stock unmodified harness, run energizes the ancillary circuits/ballast ignition circuit, start energizes the non-ballast ignition circuit
On a stock harness with IGN1 & IGN2 tied together, bypassing the ballast, the ignition circuit sees 12v in both start/run, but does the ancillary circuits also see 12v in both start/run? If that is the case, you can simply use the choke wire as the keyed 12v trigger wire for the Sniper/Fitech.
 
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