Time
Money
Quality
Pick any two
You have a rat's nest. Time for D-Con
Digital camera. Take lots of photos in bright light
Do not install new battery. Use it to check circuits BACKWARDS
Cut out damaged wires. If wires are obviously paired. Use tape and keep it that way. Get rid of bare copper and charred sections. Start with stubs. You will be grafting new wire to the studs.
Go to store and get a pair (2) of eight foot long wires with alligator clips.
Chop one wire and put a 15 amp breaker inline with that wire (got it?).
Get a multimeter and a friend. The friend will man the meter at the burned wire stubs.
Clip wires to battery posts
One at a time, connect test wires to lamp and accessory sockets.
Your friend will tell you when he finds a pair of wires that works. Mark them with masking tape and pen.
It's frustrating, time consuming, and tedious. It's worth $100 hour
Best Wishes. This is what I had to to for Good Sam and Cruise America.