Ye olde wiring harness? When to replace?

In the engine bay of my 64 & 65 A's, I made a custom wiring harnesses w/ a modern relay box. The reason was both that the factory wires were brittle and I added provisions for EFI, fan, etc.

In the cabin, I re-worked the harnesses - repaired cobbled & burnt wires, cleaned all terminals. Most cabin wiring I have seen is still fine, other than damage from short circuits and clueless owners.