Ok, I spent some time today making up these drawings with some explanation on how the wires go from the ignition switch to the coil to the distributor. This is to help explain how it all works a little better…
Let me know if this info is good – bad-- to complicated -- not really useful -- etc…
When you go to check if your wire from the ignition switch to the coil is resistive or not buy using a voltage meter. You are looking for 6-9 Volts on the positive connection on the coil but if the points are open it will not give you the correct reading it will give you 12V. If the points are closed then you will get the correct reading or you can do what I have a shown below to be sure that the circuit is complete…
If this works out good for everyone I will continue to add information to this for the ignition circuits on our trucks…
Click on the image to open it and then be sure to expand it to full size.
This shows the parts of the ignition circuit.
This is the same thing just a little simpler so hopefully easier to understand.
The coil is the same thing as a Transformer it steps up the voltage that goes out to the spark plugs. (on a side note; a transformer wont work unless the voltage is being turned off and on for DC or have AC hooked to it. It's the way it works... that is what the points are doing by opening and closing the circuit to ground.)
The Condenser is the same thing as a Capacitor (Cap) it is use here to help take the arcing out of the points when they open and close.
Updated on 1-19-08
This shows how to go about measuring the coil wire to see if it is a resistive wire or not and also gives some explanation on how a DC series circuit works.
You will see that I say to hook up a temporary wire to the Negative terminal on the coil (this is the same wire that is going to the points) and connect it to ground. This makes the circuit complete just as if the points were closed so you don't have to worry about if they are open or closed.
Or you can remove the distributor cap and turn the motor over until the points are closed, but the other way you know for sure that the circuit is complete.
Note: you never want to leave the key on in the RUN position for an extend amount of time with the points closed or with this temporary wire added, as the ignition wire (resistive wire) will get warm and over a time could burn up. It would take a while but it could happen and is something to always remember… same thing with listening to the radio with the motor off with the key in the RUN position instead of the ACC position, if the points happen to be closed or if they are almost closed you can get some arcing and wear out your points quickly too.
This shows a little more about how reading the voltage across resistors in a DC series circuit works. Also, note that lots of things act like a resistor… light bulbs are one that no one thinks of but anything that is using power has some resistance value to it in one way or another…
Anyway, let me know what you think. I take all criticism good or bad…
and if you see something that you think is wrong let me know and I will research it more as it has been 8 years after getting my electronics degree and I don’t get to use it that much in the job I have now, 
so I have to knock some of the cobwebs out once in a while. 
Yes, in the #1 circuit (first example) point C would be 0V as both leads of the meter are basically on the same point so no difference in potential. 
Not really, you made a good point that I didn't explain it there very well so it was good info for me to make it better 
