The wires will have continuity , the brush sits against armature that is contact point
As for replacing you pull spring back and rest it on motor unscrew brush and remove it with a pair of needle nose pliers they just slip into guide
Then put new brushes in the back ones you can remove cables and mounting bolts on motor and turn just enough to get them you also need to get two armature stones one course and a finishing to clean armature
Either way you need to replace them or have motor rebuilt
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