RepairPal Certified shops can diagnose and repair your 1997 Mazda MX-6. They provide transparent pricing with a minimum 12-month or 12,000-mile warranty on repairs and services.
Metal conducts electricity very very well - since the negative cable is still connected - the WIRE BRUSH is shorting the positive battery terminal cable to a metal ground...
First - you must disconnect the NEGATIVE cable BEFORE any work is attempted!
Keep in mind hydrogen gas produced by the battery is very explosive - sparks can trigger a major problem!!!
https://www.lifewire.com/dangers-of-exploding-car-battery-534782