1990 five point slow

Im new to this forum and mustangs in general. I recently bought a 1990 LX 5.0 and the owner before me put in an ignition cut off switch. He had it wired to cut off on the green/red wire between the ignition switch and fuse panel. I flipped the switch and it fried something. My radio and dash lights etc no longer work at all when i turn the key and worst of all the cat wont start. I can get it to start and everything to work if I jump it from the fuse box but have to remove the wire for the car to shut off. Anyone have a clue to i can fix this? I have checked thr fuses and changed the ignition switch but nothing. Thank you any input helps!

TrimDrip

must be a fuse link somewhere in the harness I guess.

AdderMk2

top left on the diagram... where it says "Ign Switch"

1990 five point slow

Ok so i got everything to work was a relay the guy put in before I bought it but now the only problem is when I go to shut the car off it stays running. Any reason why? Anyone have this problem before. Also the relay was for an aftermarket fan I rewired to the fuse box to turn on when the key turns on

AdderMk2

undo everything the PO did, and put it back to stock.