wiring for EFI

I have a 1970 Duster, 408 with just over 500hp. I’m planning on going efi this winter. I can follow a electric schematic, understand switches and such but that’s about it electrically. The Duster has stock wiring, no modifications. No electric add-ons like electric fans or big thumpin subwoofers, although the efi will required a electric fuel pump. I do have Crackback’s headlight relay kit. I have had pretty much all the wires forward of the front seats apart, cleaned terminals and wires, replaced where I thought it was required. That included the fuse box and the bulkhead connector.

The EFI requires a power source when the key is in both the run and cranking position. Holley can’t give me a definitive power draw, but say it’s only a couple amps. I plan on using my electric choke wire for the run power source. What can I use for when the engine is cranking? Is there a feed off the fuse box that will do both? I think I have seen a thread about using a yellow wire off the starter relay, and also a thread about a brown wire somewhere. If I have a separate run and cranking source, can I just splice them together and run it to the efi, or do I need something so all those electrons don’t go backward through the other wire, if that makes sense.

I also would like to have an shut off to the fuel pump in case of an accident. Can’t use a oil pressure switch as I need to prime the efi and with the engine off, no oil pressure so no pump. I have read about a G switch. Would that be in the main power feed to the pump, or powering the relay. Holley sniper and Fitech both have relays for the fuel pump and I was planning on using those features. Is there a g switch from some other vehicle I can wire on the power supply to the pump?

Can't answer all your questions.
I have the Fitech. Main power feed is to the Battery, with a fuse. No issues with power drain when motor is shut off for extended periods.
I tried hooking that line up elsewhere at my main power junction box (car is entirely rewired) and found it did not work.
I know for the Fitech that the fuel pump shuts off if there is no rpm signal.
I also use a denso toyota style alternator. Close to 14 volts at idle.

Ken

I have the main power direct to the battery, that is important. Not to the starter stud, or anywhere else, to the battery. My keyed 12v is triggered from my 12v coil supply. You'll need to splice IGN1 and IGN2 together for your stock wiring. If you are running a stand alone fuel pump, you can use the sensor out of a Mustang in the event of a crash. I'll edit this post later with a link. I am also running a Toyota Denso alt and I'm at a rock solid 14.3v from idle to redline.
I'm running Fitech with the FCC and it works great.

JoeSBP said:

............. My keyed 12v is triggered from my 12v coil supply. You'll need to splice IGN1 and IGN2 together for your stock wiring.

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THIS

Your ignition (and the engine bay) only has ONE "run" wire coming from the ignition switch, through the bulkhead........."run" or IGN1......AND IT GOES COLD during cranking

The original Mopar wiring has IGN2 ........normally brown......which goes from a contact on the ign switch out to the coil+ side of the ballast IT IS HOT IN START.

You must hook those two together.

CONSIDER cutting the blue where it comes out of the bulkhead connector, and putting a relay in there to handle underhood loads

Also BEFORE you do this, CHECK your running/ charging voltage at the battery. If it is much above 14V you need FIX that as it is likely due to voltage drop in the harness/ terminals/ etc

Got it, I'll splice the ign 1and 2. Again, I don't understand electrical well, but if I got those two spliced, when the blue ign 1 is powered, wouldn't that then send power to the ign 2 circuit? Or doesn't that affect anything? Overthinking it?

Is there a relay part number you would recommend to handle the underhood loads?

ken5124 said:

I know for the Fitech that the fuel pump shuts off if there is no rpm signal.


That would work for me if I was in a crash. But how do you prime the system before start? No rpm, no fuel pump?

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IGN2 only goes one place........from the ignition switch which is a separate contact .........to the coil+ side of the ballast "which you won't have" anymore.

See, there are only so many switched outputs from the ignition switch..........

ACC........hot in "run" and in accessory, dead in off or "start."
IGN1......."run" hot ONLY in the run position, not start
IGN2......."bypass" hot only in start position
START......normally yellow, fires the start relay "hot" only in start

There are some other things IGN1 feeds.....the cluster, warning lamps etc, no big deal

The reason you must tie them together, is that during cranking, one supplies 12v directly to the coil, and the other is dead. Then when you release the key to run, the "direct to coil" 12v goes dead, and the other gets 12v, which routes through the ballast, reducing voltage, and then to the coil. Together they will ensure you have a full 12v to the coil (or EFI ECU) during cranking and running

Beauty. Thanks guys!

A few amps is correct for an EFI fuel pump. In my Holley Pro-jection, that is supplied from the computer box because they only run the pump for 2 sec when first powered-up, then require an rpm signal to keep the pump running (for safety). But, they suggest installing a relay (powered off battery via a fuse) so the computer need only command the current, not supply it. I forgot how the Holley Commander 950 does it, but the harness might have such a relay. Have Holley's instructions gotten worse, or did you not read them carefully? I sure wouldn't power it off the choke circuit, nor via the key switch.

BTW, Holley's original fuel injection was designed by the guy who runs Big Stuff (sold mostly to racing teams), and the original boxes said "by MSD". Seemed with Pro-jection there was only one guy at Holley (Woody) who could answer any tech questions, and the design was very marginal. It got much better by Projection 4DI which was essentially the later Commander 950.