You can gOOgle "how to measure steering cable" and get several good hits.
Study some, measure your cable, and please order the parts from our sponsor, BoatFix.com
If your boat is an 87 and no steering parts have been changed, it's probable that you may need to replace the Helm (where your steering wheel attaches) as well as the cable. You can also upgrade to "no feedback" with a new helm also. What NFB does is let you steer the motor, but keeps the motor from being able to "steer you."
Cable is a plastic jacket over a steel shell with a steel cable inside. Yes, all of this is in strands and rust can get in there. More likely than not, it's that the lubricant has dried out, as well as possible rust or broken strands.
But also, disconnect your steering cable at the motor, and make sure the motor itself is swiveling freely in its brackets!
