I’ve got an old hunting truck that and someone decided to try to steal, but destroyed the drive column, then ripped every bit of copper wire and harness out. Now I’m just trying to straight wire it. As in push button start and a few switches in the cab. It is a 1975 4.9 inline 6. I’ve got it where I can get the starter to turn the engine (no fuse in line yet, not sure of the amperage), but it is apparently the transition year to using an ignition control module (ICM). I’ve been reading everywhere about a "resistor wire" but unable to find any and not sure if it is even part of the system as the articles are talking about Chevy engines. After a ton of frustration I have replaced everything; new distributor, rotor button, distributor cap, coil, ICM, plugs, and plug wires. I have power wired directly from the battery through a switch running to the positive side of the coil and the red wire on the ICM (the ICM has 2 wires running in, 1 red and 1 white, from my reading the white only applies when the truck is starting??? So I have nothing running to the white) the distributor has a wiring harness (somehow missed during the theft process) that goes directly to the ICM and no where else, and matches up perfectly, the only other wire left was a green wire that I read goes to the negative side of the coil. All this and I still don't get a spark when I run a plug wire directly from the coil to a plug. Just to make sure my ground is good I wrapped an extra wire around the test spark plug and ran it to the ground on the battery. I have grounded the engine and the frame to the battery. What else could I be missing?

 

You should fine a 1975 wiring diagram here:

http://ww2.justanswer.com/uploads/cr...ruckwiring.pdf

 

The "resistor wire" you hear about is a wire that runs from the ignition switch to the firewall (up under the dash). It is quite long, this wire, and usually pink. Its purpose is to reduce the current going to the coil. If I recall correctly, on the engine side of the firewall this wire splits into a brown wire that goes to the starter relay (solenoid switch) and a red/green (I think) wire that goes to the positive side of the coil. I could confirnm that for you when I look at my setup later.

 

One more thing: instead of rigging switches, you may think about picking up a universal switch, one of those with the 4 posts, that folks use for boats and the like. It will work on this system. In fact, I have one on mine. Just mounted it in the original dash hole.

 

'74 was the transition to electronic ignition for our trucks, both '74 and '75 were different and one year only ICM's, '76 and up were Duraspark II.

 

That's right, and it's hard to tell from the original post if the replacement module has the "extra" wire, the blue one, that was on the harness with the red and white ones in '75, and dropped on later units. My '75 has it. Though, I understand it will run with the unit that has just the red and white wires.

 

On re-reading, I see that the poster says that the replacement module has just the red and white wires. Wherether you need the blue, I don't know for sure. I have been told that the function served by the blue wire was incorporated internally into the module on later models, so they will work without this wire. I can tell you that, as you see in the diagram I linked, the blue wire connects to a wire that goes to the voltage regulator (the one indicated on the diagram).

 

My '75 has the additional 7th wire (blue) as well, the aftermarket replacement modules are all 6 wire units (no blue wire).

when my module went bad i tried three different brands of the new "replacement" modules, they even included instructions stating "the blue wire has been deleted, and this module will work for your application"

well needless say it did not work, at least for me anyway, i ended up buying a NOS Motorcraft module on ebay which had the original blue wire.

 

Yes, the parts manuals will also sometimes note that the 2-wire unit can be used instead, but I haven't tried it.

 

Highboy,
Where do your three wires go from the module? I understand from the diagranm I have that one goes to Run (the ignition switch), one to Start, and one to the voltage regulator. I've had mine running like this but only briefly since it had points until recently. If I recall now, not having it in front of me, my red wire goes to the Ignition switch, to the same pole as the pink resistance wire, my white ties into the wire coming from the S pole of my starter relay, and my blue to a wire coming off the voltage regulator. Does this seem right? I don't want to fry something.

 

Pick which one you need.

 

As best i can decipher the blue wire on my module goes to the ignition switch as per the schematic below....

the only info i could find on the blue wire reads as such "The blue overload shunt lead is no longer required and is eliminated because of the internal improvements in the ignition module. The ignition module now has six leads."

but as i stated in my earlier post, my truck would not fire with the newer 6 lead modules (i tried 3 different modules).

 

I like the diagram posted by gwf because it shows the actual switch and starter relay. However, it does have different coloured wires. Using the numbers and position, it seems the number 4 is the red and goes to the run pole of the switch. Number 5 is the white and goes to the start pole of the switch. Number 6 is the blue and goes to the I side of the relay. Question: does that Number 6 wire go directly there or does it connect to the wire going to the + side of the coil? It's hard to tell. And what about the wire labellled "red-green" coming off the Run pole of the switch, the one the Number 4 ties to. Where does that go from that junction?

 

I noticed that too, my wires are red, white and blue on the three lead connector, with the blue wire in the #6 position.

 

Something is confusing here:

Gwf's diagram shows the #4 wire (red in my and Highboy's case) going to a Run pole on the ignition switch, the same pole as the resistor wire. Highboy's diagram shows #4 going to Run wire also, but not the one with the resistor wire. Does this matter, as long as it goes to one or the other of those?


Gwf's diagram shows the # 5 wire (white in my and Highboy's case) going to a Start pole on the ign switch, but Highboy's diagram shows #5 going to a Run circuit. Can both be right?

On the #6 wire, they seem to agree: Gwf's diagram shows #6 *(blue in my and Highboy's case) going to a Run pole on the ignition switch, the same pole as the resistor wire, and Highboy's diagram shows #6 going to the resistor wire as well.

So, the question is, where exactly are the red and white wires, #4 and 5, supposed to go?

And, regarding gwf's diagram, where the #5 (white wire) is going to a Start pole on the ignition switch, what is the route of the #6 (blue) wire? It goes to the I pole of the starter relay, but does it just tie into the brown wire coming off that pole, or does it tie in somewhere else along the way?

Thanks guys. Hope you won't lose patience with a confused amateur.