Odometer issue

I was wondering if anyone can tell me how to fix an odometer that stopped counting miles.  Speedo works fine, but the trip and odometer doesnt.  I have done some searches but can't find an "odometer cable".  Can someone point me to a web site or give me some step by step help on how to fix this issue?  ANy idea on how much the part runs?  Thanks!

might help if you know what it is..... 1990 chevrolet half ton with 350 v8. Thanks