After studying jetfixer's diagram a bit more, there are a couple more places you could test to ensure you have a good ground for the ignition system. This test would require piercing the wiring though, which if you have a couple safety pins or needles you could pierce the insulation that way and touch your multimeter probes to needle to make contact with the wire, make sure the needle isn't touching anything other than the wire you're testing and the multimeter probe. In the image below, the green wire grounds the coil to the ICM, if you pierce the wire at the coil and at the ICM, you should have close to a 0 (zero) ohm reading. Next you could probe the black ground wire on the ICM and touch the body and frame with your other probe to make sure the ICM has a good ground to the distributor. That reading should also be close to zero ohms.

 

I don’t know the part number but I do remember testing the resistance on the new coil and it was 1.4. I will test that jumper wire tomorrow after work. I did just test ohm on the removed ignition switch plug, from resistor wire to red ICM wire, it was 80 ohms. Are they even suppose to be connected? Individually they have less than 2 ohms each. What does that mean?

 

Per the schematic above, the ignition switch feeds 12v+ to the ICM and to the coil through the resistance wire when in run position.

From ignition switch to coil you should have roughly 1.1 ohms due to resistance wire. From ignition switch to the ICM there should be close to 0 ohms as it should be feeding a full 12v+ to the ICM. In the start position, the resistance wire is bypassed and the coil is provided 12v+ and the white wire feeds the ICM the voltage it needs to run. From my understanding feeding the white wire to power ICM versus the red wire, basically tells the ICM to retard the ignition timing to help with startup. Once key is back in run position the ICM gets power from the red wire.

The ground for the coil is controlled through the ICM and that is how the ICM controls when the coil fires. The way a coil works is you send 12v+ to primary side of the coil and that builds up a charge, at a certain time the ICM disrupts the ground side shutting off the current flow on the primary side of the coil that has been building up a charge and a magnetic field. By killing the power to that circuit the magnetic field collapses which induces current into the secondary windings which are finer, tighter and more numerous windings than the primary side. The induction caused by the collapse energizes the secondary side of the coil sending high voltage, much higher than 12v, enough to overcome the resistance inherent in plug wires and spark plugs themselves, to the distributor which then sends the charge to whichever spark plug the distributor is lined up with at the time. The power transformer on the utility pole outside your house works on the same principal but in the opposite direction to reduce the very high voltage used to push power over the grid long distances to a more reasonable 240v used in residential homes.

Think of voltage as the pressure pushing the electrons through a circuit. The Amperage is the volume of electrons being pushed and anything that restricts that flow is what we call resistance. Bigger wire, bigger pipe, more flow and less resistance. If you have a lot of resistance you need a lot of pressure to push the electrons through the pipe.

The ICM opens the ground circuit for the coil based on the signal sent to it from the magnetic pickup inside the distributor that sends a small voltage signal as the stator passes by the magnet that is part of the pickup coil is wrapped around. Your alternator works on the same principle passing magnets by coils of wires inducing voltage and current in the wires ultimately creating electrical current to charge your battery.

If there is an issue with the magnetic pickup inside the distributor the ICM won't "know" when to open the ground circuit for the coil causing the magnetic field to collapse which ultimately creates the spark to fire your engine.

Hope that helps you understand a bit better what you're testing and how the system ultimately works. In older points style ignition, the points performed the function of both the ICM and magnetic pickup coil inside the distributor. The points themselves are a mechanical switch opened by a cam inside the distributor where the stator is located in your distributor, when the points opened that opened the ground circuit on the coil, causing the collapse of magnetic field necessary to induce current in the secondary windings.

 

Update.

I jumped “batt” to the terminal with the resistor wire and measured at he coil. From positive coil to negative coil I got nothing, no continuity. From positive coil to engine(as ground) I got 11.something volts. That means the ignition switch is bad, right? Are we back to saying the resistor wire is bad since I’m getting battery volts +/-1 at the coil?

P.S. I forgot to measure ohms. Is that even necessary at this point?

 

Measuring across the coil terminals and showing nothing doesn't surprise me. If the ICM has the ground circuit open there would be no current flow and would show zero volts as you saw. Going from positive terminal to ground completes the circuit allowing current flow and you saw that on the meter with your 11v reading. There is potentially an issue with the resistor wire because you should be getting 6-9 volts there due to the resistor wire, but I wouldn't worry about that right now. You have proved you can get higher voltage at the coil bypassing the switch.

With the switch out, with meter set to ohms, test the continuity across the same terminals on the switch that plug in where you jumped battery to coil resistor wire. With key in off position, you should see zero continuity (infinite resistance). With the key in run position you should have full continuity with zero ohms. If you have any resistance reading at all across those terminals I suspect there is an internal issue with your switch. If it tests good, shake it to stimulate road vibrations and turn the key on/off a few times then test it again to see if your measurements change.

Seems you might be narrowing down where the issue is and so far you're only out some time aside from the coil and ICM you already bought, which are good to have spares of anyway.

 

FIXED/SOLVED

I tested the ignition switch on my workbench. Infinite resistance/no continuity with key in off position, as expected. In run position the ohms jumped around A LOT. The lowest I saw was 1.2(for less than one second) the highest I saw was over 100(for less than one second) but it mostly bounced between 3.something and 10.something. I tested the new switch(from oreillys for $21!) and it was as steady as I could hold my hands at 0.7 ohms. I installed the switch and plugged everything back in. In run position I tested the volts at positive coil to negative coil and got high 5’s(I don’t remember the exact number). I then put the negative probe on the engine block and the volts went up to 6.something. It may not be within specs of 7-9 but it’s WAY better than it was. I reassembled everything and ran some errands to test it on the road. Everything went perfect for 30 minutes! My only problem was when I sat in the chick-fil-a drive through too long and the engine began to stumble, completely unrelated to this issue.

 

Good to hear you got it solved. 6-8v is the spec as I recall and if you're getting 6 volts at an idle and the issue seems to be resolved I think you're good to go. At higher RPM once the alternator is spinning faster you probably have a bit more voltage being pushed to the coil at that point.

Stumbling after idling for a long period of time isn't surprising. Things are getting pretty well heat soaked, there's not much air flow and fuel can start to vaporize.

 

Glad it's sorted! That was a lot of work digging down into the harness.

Not sure this is a universal truth, but in my experience, a coil marked "for use with 12v" is designed for 12v and NOT a resistor wire. Glad you got it working, but I would still look into that aspect of the coil you bought. Was it specifically for your truck?
And regarding the resistor wire feeding both the coil and the ICM, that's only true for some very few models. If you look again at the diagram posted, the ICM is connected to the Red w/green wire BEFORE the resistor. Only the coil gets the resistance, and the ICM gets the full 12 volts.
Earlier when you were showing the two Red wires you were testing, those sure looked like the Red w/blue wires. Not the Red w/green wires.
If they were indeed Red w/blue stripes, those are the START signal wires only. One goes to the White wire on the ICM and the other goes to the "S" post on the starter relay and is what causes the starter to spin.

And going back to the resistance between the Orange and Purple wires of the distributor stator, you should see an ohm reading of between 400 and 700 ohms. If it's outside of those parameters, or even close to the limits, it's probably about done with it's life and should be replaced.

Sorry if you guys already touched on all of that. If so, I just missed it when reading the posts.

Paul

 

The stator moves constantly so the wires have to flex. The vacuum advance is what moves the plate and stator.