For example If I was working on a 70 Charger and wiring a MSD ignition I would trace out all the wires nec to do the job. In this case after I color the wires, I can see that the wires I need are the Dark Blue with the white tracer and the Brown wire.
From one of the post here (today) I read that I need the Brown wire and the Blue wire with the white tracer connected together if I remove the resister. I then connect this to the small wire on the MSD unit
If I did not want to remove the resistor I could just hook the small red wire up to the Blue wire that leads to the coil.
If I did not want to wire it at the resistor I can find the same wires in the middle connector at the firewall.
If I wanted to put it inside I would follow the same two wires at the bulkhead to the inside of the and tap the wires there.
click the link to see a bigger pic click again to see even bigger.
Sounds really hard but if you do it a step at a time it is not hard at all.