I've just switched to a diesel engine, and need a wire that goes hot as soon as I turn the key to start, and stays that way continuously until I turn the key to off. Not one on the start bypass circuit. This is for my fuel shutoff solenoid, so it can not go off at any time, or the engine will immediately die.

Which color wire, on the ignition switch, would satisfy this need?

79 F150 4x4

Thanks, Alex

 

1973-1979 Ford Truck Wiring Diagrams & Schematics - FORDification.net

 

There's no point in showing wiring diagrams. No wire anywhere is hot in START and RUN. These are independent poles of the ignition switch. Such a requirement only appears in two places from the factory: the ignition module, where the separate hot-in-RUN and hot-in-START inputs are electrically isolated internally by the module, and the ignition coil, where the additional hot-in-START signal is provided by the dedicated 'I' terminal of the starter solenoid. This terminal must never be loaded.

Please describe exactly what it is you're doing. Are you setting up an electric fuel pump? If so, there's a different way you should go about it.

 

Fuel shutoff solenoid. It's a spring loaded safety switch that, unless wired in to + 12v, cuts off the fuel. It's both an easy way to kill the engine, and a good safety mech. There's got to be a simple enough way to power it both while cranking and running.

 

I hesitate to tell what wires to use as they are unfused prior to entering the fuse block.



I needed the same circuit for my fuel injection swap. my 74 is a dash mounted switch and the diagrams only showed the later models with the steering column switch having this circuit.

Funny thing was the switch has the circuit.
Either the engineers that drew the diagram only showed what was being used in the circuit, not what was present. OR that the switch I have installed is not the OEM switch.

I don't have experience in your 79 version.
And I am currently on the road working without access to the diagrams I made.
But red/green should be the one you're after (it's red/green near the switch then changes before entering the splice.)

The splice on my 74 was just to the right of the heater controls in the main bundle. I removed the resistor wire from the splice and installed a 5amp inline fused circuit for needed start/run and it runs just great.

I don't know the electrical load of your fuel solenoid. It's up to you to do a load analysis and include proper circuit protection.

FMC if you look at the 79 diagram closely you'll see the wiper in that set of contacts is shaped differently to show that it hits two sets of contacts start/run

 

Brigart, thanks for the clarification; that's good information. Apologies for the confusion (total oversight on my part).