12 Volt switched source

[mackseal 10]

I have a 302 with a Sniper EFI which requires a 12 volt switched power source.  Does anyone know of a good and reliable source? I was looking at the back of the ignition switch, however it appears the post is not threaded and under the harness connector.  Does anyone know if this could be modified or used? Drawings/diagram and or a picture of your setup would be great! Thanks in advance.

[Midlife 814]

The green/red wire at the voltage regulator is always a RUN-only power line. 

[barnett468 418]

the ignition wire to the coil is also a switched wire but for 12 volts you need to tie into it next to the ignition switch.

[Mach1 Driver 560]

Since this is a common question I added a page to my Mustang Schematic. If interested go to How Tos, A Real Schematic, page 5.

There are three fuses connected to the ignition switch and powered on in "Accy" and "On" . They are 1, 2, and 3. On my Mustang #2 has a 20A fuse that goes to an accessory plug that is just hanging here ready to be used. Its my understanding that this fuse was used on a bunch of Cougar options.

Edit, I should add that this is not a good place to connect an EFI for two reasons; 1) its not on in "start" and 2) its on in "accessory"- when the EFI shouldn't be powered-up. It is a good place to connect common accessories that aren't engine related. I'll update page 5 to show how to connect to the "start/on" side of the ignition switch...or maybe add a page 6.

[Midlife 814]

I don't like to use the term "switched power" as that can mean either ACC or RUN-only power.  Your schematic, Page 5, shows ACC power.

Electric chokes are best to use RUN-only power.  EFI power source can be iffy with ACC power.  You see, when the key is in the CRANK position, the ignition switch causes the ACC power to be cut off and only RUN-only power lines are active. 

[larryc94 38]

2 hours ago, Midlife said:

I don't like to use the term "switched power" as that can mean either ACC or RUN-only power.  Your schematic, Page 5, shows ACC power.

Electric chokes are best to use RUN-only power.  EFI power source can be iffy with ACC power.  You see, when the key is in the CRANK position, the ignition switch causes the ACC power to be cut off and only RUN-only power lines are active. 

That green/red provides power in the crank/run  position which the EFI needs to start.  Also that wire is in the harness that exits the firewall and runs along the pass shock tower brace.  A very convenient place to  open that harness to tap into that green/red wire that goes to the regulator.

Make sure you solder and shrink wrap all connections.  Wire taps and crimp connectors(solderless terminals) are unreliable. Biggest cause of failed installs

[Midlife 814]

I'll agree with you that most crimp connectors you find in part stores are pretty crappy, but if you use uninsulated butt connectors with the proper tools and shrink tubing, the crimps are as reliable as solder.  That's how the US Air Force and NAVAIR do their wiring repairs. 

[larryc94 38]

42 minutes ago, Midlife said:

I'll agree with you that most crimp connectors you find in part stores are pretty crappy, but if you use uninsulated butt connectors with the proper tools and shrink tubing, the crimps are as reliable as solder.  That's how the US Air Force and NAVAIR do their wiring repairs. 

Agree if you (and I'm sure you do) use OEM type open barrel connector with the proper crimping they are better than solder

[Mach1 Driver 560]

14 hours ago, Midlife said:

I don't like to use the term "switched power" as that can mean either ACC or RUN-only power.  Your schematic, Page 5, shows ACC power.

Electric chokes are best to use RUN-only power.  EFI power source can be iffy with ACC power.  You see, when the key is in the CRANK position, the ignition switch causes the ACC power to be cut off and only RUN-only power lines are active. 

Mid yes I see your point, ignition switch B to A is on in the "accessory" AND "on" positions, while ignition switch B to C is on in "start" and "on". It is a better choice for the EFI, but is unfused.  It exits the ignition switch on C with wire #16 red/green stripe, goes to the plug for the tach. It goes through the tach or if no tach directly to 16A the pink resistor wire. You want to make the connection before 16A.

[Mach1 Driver 560]

See page 5 of "A Real Schematic" in "How To's" section. It shows how to connect to switched power with "accy/on" for loads like radios etc, and "start/on" for things like an EFI. Please note that you can't run unlimited power through any of these circuits, so be aware of how much power you will draw and use a relay if necessary to divert the load back to the battery through separate wires.

[Vicfreg 771]

Your EFI probably needs a "hot" during the "start" and "run" positions.   My FiTech is that way.  I used an AAW harness, so no issues.   There is a recent thread on an electric choke power source that led to an extensive exchange on this topic.  I would look at that, it will save you some time.

[mackseal 10]

Thanks, for the suggestion. I will definately check it out.

[gordonr 4]

I would look into disconnecting  coil positive  and running that power to the sniper ignition "on" and  also a supply for the activation to an ignition coil power supply rerouted  thru a relay.  Relay internal coil activation draws 250 mA so you will have no issues with the resistance wire  in the factory wiring and gain the ignition power supply when cranking to the sniper. Seems as thou Holley doen't want the same power line feeding the Sniper as the ignition coil.