Hard to say what may have caused that, there have been multiple people over the years with fires from that fuse box area and nobody really knows why. I’d guess aftermarket added junk contribute but no one really knows.
That harness is the firewall bulkhead harness which has the automatic transmission torque converter lockup on it, since you have a 94. This means you’ll need a harness from any 94-95. You don’t need the engine portion, your engine harness will plug into whatever you buy.
The bad part is that most people lost the whole engine plus firewall harness as one giant engine harness which is technically incorrect and will get you more than you need for more money than necessary. But that might be what you have to buy to get what you need.
As long as you get the harness with the long rectangular relay box and it’s 94-95 so it has the torque converter relay, you’ll be fine. That harness just runs from the relay box, up to the firewall, across the firewall and plugs into the bulkhead connector with a bolt. It hands off to the engine harness at one connector at the firewall, and one connector near the battery/distributor along with an alternator charge cable.