The ends of these two cables look the same at a cursory glance, but when you get them up close to eachother, you realize that the ends of a Campagnolo brake cable and a Shimano road brake cable are not the same. The Campy cable end on the left is smaller in diameter, and also shorter in length. I didn't realize this until I tried to install the Shimano cable on my Campy bike. Catalog ads tend not to say "Shimano compatible only", and the cables install pretty much the same way, so who would have thought them to be different?
To resolve my problem, I ground down the Shimano cable and stuffed it into my brake lever. Will it hold? I'll let you guys know. Until then, I have at least one lever with a regolamentare cable in it so that'll stop me.