Apply 6 volts to the wires and see what happens. If they look normal, they're 6 volts. If very dim they're 12 volts.
i'D SAY 6 VOLT'ERS, THEY LOOK THE SAME AS THE ONE i GOT FROM MY gRANDFATHERS STUFF. i HAVE ONE FOR A SPARE IF YOU ARE INTERESTED, PM ME. MBMOPAR
MoPar accesory lamps were manufactured for Chrysler by the Unity folks. They are still in business building those lovely spotlights the cops use to kill your night vision. They also made Logo'ed lighting for other manufactures as well. Looks like the manufacturers stamp says December 14, 1940 to me wire gause and clth insulation supports 6v. nice looking lamps. I have a similar pair made by Dietz that my Dad had on several of his cars in the 40's. http://www.unityusa.com/