I read everywhere that you can create problems if your plug wires are touching one another. I see all of these wire separators online and at car shows that attach to the valve cover and separate wires nicely but up near the distributor on every car I've ever seen, the wires are criss/crossing all over the place. Its just about impossible to run 8 wires and have NONE of them touch. Anyone explain this to me?

 

new quality wires will be ok touching each other. the problem comes when the wires get old and start cracking. they lose the ability to hold the spark in and if touching another wire the spark will transfer from one wire to the other causing a missfire. not sure about anything caused by the electricity like magnetic fields or stuff like that.

 

...And also if you have "leaky" wires, the problem can be made worse if the wires are touching while laying "in line" with each other, as opposed to being twisted around or at an angle to each other.

 

As 69 said. The problem occurs when wires touching each other run parallel to each other. One wire can then induce voltage into the other, like a cheap transformer. This does not happen when the wires cross each other.