I am posting this here because nothing else makes sense

As we all know our cars are old. I would do a thorough inspection of the wiring under the dash could have some mouse eaten wires under there with you working on the wiring something could have shorted out causing the fire. Glad you didn`t have any major damage or injury. Let this be a wake up call for anyone not having a good fire extinguisher in their car/garage/workshops & home.