I'm so glad that you pointed to the relay that you did , up in the top left, (R1) because I've watched other videos with very similar aged Ford Focuses, and there pointing to R8 which is the 4th in line , smaller relays, right in the middle, so I was starting to 2nd guess myself when I looked at my manual and thought it really should be R1. Thanks for confirming!!! My manual also says to disconnect my battery but every video I've watched no one is disconnecting the battery 1st , so I'm really wondering if its a safety issue that needs to be done, because if it were nobody would be living through any of their demonstration videos lol!
That wire is the ground wire for the ECU / PCM which is the car's computer, without that wire or the wire being damaged the computer does not get proper grounding to make a connection to start the car.
Glad to know that as a possible issue in the future, I think I’ll just keep a replacement of threaded copper coiled wire and a soldering gun just in case I need to heat the coil to make my own to replace it. $2.00 fix