Brake cables are different from shift cables. See picture below.

A. Campagnolo Brake Cable - For most drop bar brake levers - A & B generally interchangeable
B. Shimano Brake Cable - See above
C. Mountain Brake Cable - Most upright bar levers
D. Shimano Shift Lever Cable - Larger head will not fit Campagnolo levers. Should work with Suntour levers???
E. Campagnolo Shift Lever Cable - Fits most levers but D. fits Shimano levers better

Most Weinmann levers require these ferrules - Dia-Compe too. See below.

Buy premium quality cables, preferably made of stainless steel. Jagwire makes good cables. Better shops sell cables and housing separately rather than just kits. Usually less money too.

Buy new brake cable housing with a friction reducing liner. I grease the cables as well. It's a messy job but the results are well worth it.

You should also consider replacing the brake pads too. They get old and hard and don't work as well as modern pads made of newer rubber compounds.

There's lot's of little tricks to make your brakes work better. Search Google for "replacing brake cables". You'll find a lot of info that doesn't apply to your brakes but look around, it's how you learn new things.

Chas.