Wiring Question

[lalessi1]

This is kinda lazy but I am planning my EFI install and I have a question. Does the "ON" terminal on the ignition switch stay on while cranking the engine? I know the resistor was bypassed with the extra terminal on the starter solenoid as originally wired so i am thinking out loud. (I noticed that my fuel pressure goes to zero while cranking the engine.) I ran a dedicated wire straight to the coil when I first got the car to make sure I always had spark but now I am a little confused.

[gasman826]

I looked around the engine compartment for a 'KEY ON' 12V source.  There is one to the coil + wire and another to the voltage regulator.  I hooked an electric choke to the plus side of the coil.  There was so much draw that the engine would stumble under a load.  To fix this, I installed an under hood KEY ON relay.  The relay offers a KEY ON source for upgrades (electric fans, choke, EFI, fuel pump, wipers, radio, headlight, etc).  I could have cheated and spliced into the coil wire but I ran a home-run wire to the ignition switch.  The relay draws very low amps to activate.

[Ford Blue blood]

I'm with Gary on this.  Pulling 12V off the coil will reduce drive ability majorly.  Pulling off the voltage regulator ( I terminal) will cause a flickering charge light (don't ask how I know this).

The run terminal on the stock ignition switch does stay hot while cranking.  This is a good place to pick up 12V to turn on a "run" relay.  The power source for the switched part of the rely should be off the battery side of the starter solenoid.

I pulled the relay on 12V from the input side of the ballast resistor.  It is the side that has only one wire on it.

[lalessi1]

Thank for the help guys! I never considered a relay for a switched ON source that and that sounds like a great idea. The ECU requires a switched 12V source as well as a direct connection to the battery. I will run a direct dedicated line to the ignition switch for the ECU. The instructions were specific that the switched 12V source STAYS ON while cranking, hence my question. I have relays for my fans, fuel pump, and A/C compressor. The ECU has a built in relay for the fuel pump and I am going to use Bosch relays instead of the SMP ones I am using now. I can also ditch the fan controller since that function is handle by the ECU as well. 

[81TTA]

I also wired an "ignition" relay off of the input side of the ballast resistor.  The small amount of current needed to actuate the relay hasn't affected the coil's performance. 

One thing to consider if you're not doing it already...  As you mentioned, there always seems to be "another" electrical thing to hook up that needs relays/fuses.  It's easy to do these one-by-one and have inline fuses and relays located all over the car or wiring harness.  There are aftermarket fuse blocks available that make putting all these in one place easy and neat.  I have one under the hood for "outside" devices like cooling fan, wiper motor, ignition/fuel shutoff and reverse lights.  There's another mounted by the kickpanel for "inside" devices like the radio and CD player. 

Took some extra time to do add these blocks.  But, it makes life so much easier if anything needs to be added.  And, having one place to look for a potential blown fuse is also very helpful.

[Ford Blue blood]

When building the Ranchero I decided to use "Run" and "ACC" relays to eliminate the extra load stuff puts on the stock ignition switch.  Mounted the relays ( 30 Amps ) in the drivers kick panel.  Also mounted Hi/low head light relays.