Burnt wire

Could be the fusible link. That’s what it looks like being a little way from the bulkhead connector.

Often the connectors in the bulkhead connection overheat and melt stuff, usually due to corrosion.
There are basically three wires that usually get heat damage near the bulkhead connector.
1. The big power wire (fusible link) going to the amp meter on the dash in the passenger compartment.
2. They big wire coming from the amp meter into the engine compartment
3. )The ignition wire