From the factory they had on the plug wires the number of the cylinder the plug wire went to and it also had the wording " GM Electronic Suppression" So for Example on the #4 plug wire you would see printed on it, " 4 Gm Electronic Suppression" Now ONLY the factory wires had these markings, but highway stars did a run of them that were an exact match to the factory originals and that's what I have. I can post a picture of them up later today.