There is normally a plug/socket wiring diagram label on the radio casing.
Using a multi-meter or test lamp this will prove the battery and chassis/earth at the wiring socket.
this site may be useful
http://www.tehnomagazin.com/Auto-radio-car-connector/PHILIPS-Car-Radio-Wiring-Connector.htm
If it`s the car wiring then a Haynes Workshop Manual will be required.
RegWorts
October 2008