1985 cadillac eldorado

Blower motor quit working…obvious, put in a new blower motor, however my mechanic friend did some checking and found that if he attached a wire from the positive side of th battery to the ground terminal on the blower motor, it worked, this does not make sense to me nor to him any help would be appreciated

On any DC motor, if you reverse voltage polarity it’ll cause the motor to run backwards.

Tester