My experience with the problem
After determining that a ground wire to the last lamp on a 4 lamp circuit was faulty, I thought I could reave a new wire through by attaching it to the old one. No way! On my older 27 (and I guess the other Catalila models of that era) the wiring harness was simply glassed in between the liner and the core. That's a common cost saving technique for boats of our quality level. So it was impossible to remove, much less replace. My suggestion is to use the good existing wiring as best you can. Replace the damaged wire with external wires and try concealing them with an attractive conduit. An inexpensive continuity tester will help you determine the damaged circuits.
