Electrical help needed, underdash wiring is a disaster

Karl Nicholson said
The brake lights on my dads 65 fish stop working so I checked the wiring at the tail lights. Eventually ended up under the dash and it's a mess of poorly added new wires with heat shrink and butt splices etc. The fuse panel seems to be bypassed with inline fuses added.
Other than buying a new harness for $600 plus dollars which I can't afford, what's the best way to clean this up and make it safe and reliable? Trying to figure out where to start..

I will say we had a similar situation with my son's 70 Dart. I would suggest, if you have the time and patience, pull the harness and go through the harness and do the repairs. It really wasn't that difficult, just time consuming and a bit tough on the back removing and installing it. It also helps if you have a large work bench to stretch the harness out and label everything and check continuity and to do proper repairs where needed.

Good Luck!