[morzh]

First there is no positive or negative. The motor is AC.
Second. Simply buzz the wires. Cannot be simpler than that. Unplug and start with ohmmmeter all the way from cord to chassis. As long as you methodically do it piece by piece I guarantee you will find it within 10 minutes.

One more thing: you have hot chassis radio, so the chassis is connected through the switch which could be dirty. It could be enough for the radio to work but the motor requires more current and might not work.

So, check the power switch and see if it is a true short of say tens of ohms.