Clean 12v switched source that is hot cranking and running

-

cdwmotorsports

Well-Known Member
Joined
May 22, 2004
Messages
305
Reaction score
54
Location
Martinsville , IN
I’m installing a Holley Stealth Super Sniper 550-877 FI kit and need a clean 12v switched source that is hot cranking and running. Instructions specifically say not to use the ignition coil, audio systems etc.

where can I pull this from?
 
There is none

There is only one switched ignition lead into the engine "room" and that is IGN1 usually dark blue. It powers the ballast resistor, depending on year, the VR, the alternator field, and electric choke, and smog doo dads if equipped. THIS GOES DEAD during cranking

The ignition bypass, IGN2, usually brown, connects to the coil+ side of the ballast. This comes direct from the ign switch AND IS ONLY ACTIVE during cranking. It is SEPARATE from the yellow "crank" wire that triggers the start relay.

What you must do is either change to an ignition system that DOES NOT use a ballast resistor, or else go through "other shenanigans"

With an ignition system that does not use a ballast, jumper the ballast resistor terminals together and use the old coil+ wire for your feed, "basic."

But BETTER is to use that wire to trigger a relay, and feed all underhood loads off the relay. This is because of common "harness voltage drop" which lowers voltage to the VR and causes over-voltage

Electrically cut the blue "ignition run" wire coming out of the engine bay bulkhead and wire the bulkhead end to trigger a relay. Connect the engine bay end of the cut wire to the load output of the relay. Power the relay contact off the starter relay through a big fuse/ breaker.

But since you are going to jumper the IGN1 and IGN2, you want to add IGN2 to the relay trigger.

Find and download a shop manual and wiring diagrams, from MyMopar, free

---------------------------------------------------------------------------------------

If for some reason you are going to retain an ignition which uses a ballast, now you must "do shenanigans." Since the IGN1 goes dead in start, but is alive in "run" you MUST tap into that for your EFI. In order to get voltage during cranking, you need to "add" the IGN2 WITHOUT causing a feedback/ interaction between the two. There are a few ways to do that.

One is to add a relay in parallel with the starter relay, that is, wire the coil of the new relay to the coil of the start relay, so the two fire up together. Power that relay'z contact, and run the load output over to your IGN1 going to the EFI.

Yet another way is to tap off either the IGN2 or START wire and use a big diode to isolate. maybe a 5A 50V rectifier diode. Hook the end of the diode with the bar designator to the IGN1 tap and connect the remaining end to the START wire or to the IGN2 feed.
 
Last edited:
By the way this problem is ALSO common with GM and Ferd. I don't know why the EFI people did not do a better job of addressing this problem. For example, older GM has the S and I terminals down on the starter solenoid. The "I" terminal does the same job as the IGN2 circuit in the Mopar ignition switch

Same is true of Ford. The "I" terminal on older Ford fender starter relay feeds "hot" full 12V to the coil during cranking.

The difference is that Mopar applied this circuit right in the ignition switch, instead of the starter relay/ solenoid.
 
I already have an ignition system that doesn’t use a ballast resistor. MSD pro billet distributor and 6AL box. Is there a wiring diagram for wiring the relay? I’m better with pictures than words when it comes to electrical.
 
Yes. You must be careful depending on how you do this. Let's say you are not going to install an extra relay. Just jumper the ballast wires and use the original coil+ wire to feed the EFI

But to get very specific you need to post what it is that you are working on
 
72 Demon with a big block, factory wiring is all still there. Has two separate fuse blocks one feeding 12v hot stuff (fuel pump, gauge lights, ignition box) and one that is powered from factory radio power it runs the electric fan controller.
 
Also I have relays and have no issue wiring one in. Relay diagrams are what work best for me rather than me trying to figure out what wire goes to what terminal
 
I’ve heard that wiring the blue and brown wires together works, but some systems have a problem when power drops out on both when the switch goes from Start to Run. The gap between the contacts can cause a no power situation and some PCM’s see this as the car has shut off and it needs to see a start event again before it runs, resulting in a car that fires but won’t stay running.

Any options for this Del?
 
I have not experienced this with the Holley I ran the old old Holley "pro-jection", the slightly newer Commander 950, and finally, the Holley HP
 
I have not experienced this with the Holley I ran the old old Holley "pro-jection", the slightly newer Commander 950, and finally, the Holley HP

Maybe it is the G3 Hemi swaps that I have heard of having an issue? Not sure, just sticks in my head that it can be a problem in some cases.

At the same time, I wonder sometimes at the things that stick in my head so maybe it is an urban myth?

Who knows, just tossing it out in case it somehow helps the guy.
 
I'm not much of a designer, but there's no reason you could not buy or build a little delay circuit that runs off IGN1 / IGN2 and will hold that "on" for say, 1/4 or 1/2 second before dropping off line. That would take care of any delay or spike between the switchover from IGN2 back to IGN1 and yet would not be so long as to cause a problem at shutdown.

A "redneck" way to do this is with a large capacitor and diode

vbXaC0wx9ys4fwA2LY46rkGMydY_CP7mi8N9Mv5lf4y0-hVDCCK5rx4mnNV_EMHM1toOOTWr1v4ndaFudGwsGs8QBFBs.gif


But for this to be effective you need a more delicate relay with a high resistance coil that draws less current.

How this works is, the tag end of the diode would be connected to IGN1/ IGN2. When that goes dead, the diode prevents the cap from discharging into the the rest of the harness. The cap discharges into the relay coil, holding it engaged fro a short time. This would be a "try it" setup you would need a parts "junk box" to get things to work
 
A short search came up with this

Time Delay on Release Relay - 12V DC, 30 Amp

But they are showing 2 sec as the minimum delay. That would not work. Let's say your throttle stuck and it started revving to the moon. By the time you got to the switch, turned off, then WAITED ANOTHER TWO seconds, that ***** would have rods and pistons up through the hood LOL

But this is the type of thing

Maybe this one

Hella Time Delay on Release Relay - 12V DC

This one, more expensive, from Grainger

https://www.grainger.com/product/DAYTON-Single-Function-Timing-Relay-24EP44
 
I'm running the sniper 4150. I'm running all 12v switched off of a fused power distribution block that has a 100A relay I ordered from Amazon to help power up the sniper EFI when I turn on the master power switch then a secondary I can kill if I have a malfunction on the drag strip. I'll see if I can draw up a basic schematic tomorrow.
 
I'm running the sniper 4150. I'm running all 12v switched off of a fused power distribution block that has a 100A relay I ordered from Amazon to help power up the sniper EFI when I turn on the master power switch then a secondary I can kill if I have a malfunction on the drag strip. I'll see if I can draw up a basic schematic tomorrow.

this sounds like what I’m looking for.
 
How ' bout a super clean 12V source that is isolated from the battery itself? run a 2nd 7AH 12V battery on a switching relay and once the car is started, switch the power back to the 'line' power. could probably rig this up with 2-3 relays and some thought. Just need to figure out how to switch between power sources without any interruption, like a small bit of overlap or some type of switching relay that does that by design. The Sniper system doesn't take gobs of power to run and those 7AH batteries can kick out a lot of amps. Could rig a kill switch in there too if you want to run the sniper on auxilliary power the whole run. IIRC MSD draws an amp per 1000 RPM if that helps any.
 
How ' bout a super clean 12V source that is isolated from the battery itself? run a 2nd 7AH 12V battery on a switching relay and once the car is started, switch the power back to the 'line' power. could probably rig this up with 2-3 relays and some thought. Just need to figure out how to switch between power sources without any interruption, like a small bit of overlap or some type of switching relay that does that by design. The Sniper system doesn't take gobs of power to run and those 7AH batteries can kick out a lot of amps. Could rig a kill switch in there too if you want to run the sniper on auxilliary power the whole run. IIRC MSD draws an amp per 1000 RPM if that helps any.

That sounds like more lbs than I’m willing to add, never mind not following the KISS rule.
 
I'm running the sniper 4150. I'm running all 12v switched off of a fused power distribution block that has a 100A relay I ordered from Amazon to help power up the sniper EFI when I turn on the master power switch then a secondary I can kill if I have a malfunction on the drag strip. I'll see if I can draw up a basic schematic tomorrow.

Any luck with the drawing?
 
I'm running the sniper 4150. I'm running all 12v switched off of a fused power distribution block that has a 100A relay I ordered from Amazon to help power up the sniper EFI when I turn on the master power switch then a secondary I can kill if I have a malfunction on the drag strip. I'll see if I can draw up a basic schematic tomorrow.


Any luck with this drawing Hazard County 29?
 
Any luck with this drawing Hazard County 29?

@67Dart273 gave a great explanation.

I just got done doing this to my 1969 dart swinger; I added a relay to my electronic ignition MSD 6AL w/o efi and no ballast resistor. I connected the dark blue and brown wires from the bulkhead together and triggered a relay. The directions I followed I found in 4x4 forums somewhere. It uses two relays to wire my ignition because I also included a kill switch/cutoff. I also wired for an electronic fuel pump; for priming only but can run if mech fails.

upload_2020-9-15_15-48-46.png
 
@67Dart273 gave a great explanation.

I just got done doing this to my 1969 dart swinger; I added a relay to my electronic ignition MSD 6AL w/o efi and no ballast resistor. I connected the dark blue and brown wires from the bulkhead together and triggered a relay. The directions I followed I found in 4x4 forums somewhere. It uses two relays to wire my ignition because I also included a kill switch/cutoff. I also wired for an electronic fuel pump; for priming only but can run if mech fails.

View attachment 1715595870

I don’t disagree his explanation is good. I’m a visual person, you can tell me something all day or you can show me once.
 
@67Dart273 gave a great explanation.

I just got done doing this to my 1969 dart swinger; I added a relay to my electronic ignition MSD 6AL w/o efi and no ballast resistor. I connected the dark blue and brown wires from the bulkhead together and triggered a relay. The directions I followed I found in 4x4 forums somewhere. It uses two relays to wire my ignition because I also included a kill switch/cutoff. I also wired for an electronic fuel pump; for priming only but can run if mech fails.

View attachment 1715595870

So what exactly did you just get done doing to your Dart? I already have a pro- billet dist. and a 6AL. I’m trying to find a place to wire the pink wire on a Holley EFI setup.
 
@67Dart273 gave a great explanation.

I just got done doing this to my 1969 dart swinger; I added a relay to my electronic ignition MSD 6AL w/o efi and no ballast resistor. I connected the dark blue and brown wires from the bulkhead together and triggered a relay. The directions I followed I found in 4x4 forums somewhere. It uses two relays to wire my ignition because I also included a kill switch/cutoff. I also wired for an electronic fuel pump; for priming only but can run if mech fails.

View attachment 1715595870

I don’t understand the need for two relays?
I don’t see anything in your diagram that shows where the “dark blue and brown wires” are on either relay....
 
-
Back
Top