Classic/Antique Car Repair: 1951 GMC 1 ton, stock truck, ammeter

Question
Is this truck negative or positive ground?Totally stock truck.

Answer
According to my best sources here it should be a negative ground. On any vehicle pre electronics such as electronic ignition, alternators, and computers, a battery that is installed backwards can be detected before the ignition switch is turned on. Simply turn on the head lights and check the ammeter. If the needle has swung to the plus or charge side the battery is in backwards and no damage has been done. If the needle has swung to the negative side the battery is in correctly. Good Luck.
Brad