To keep the 1947-1955 GM trucks base price low, their 6 volt cigarette lighter was a dealer accessory. The vehicle always came from the factory with a round blank out plug at the lower center of the dash.
To save tooling costs both the Chevrolet and GMC truck divisions used the same lighter as was found in Chevrolet’s passenger car. It did not match other knobs in the cab. Its double ring chrome head is exclusive to General Motors though it does not carry their logo. They are often seen at swap meets and flea markets mixed with lighter accumulations from all makes. The chrome head is easily unscrewed when a replacement heating element is needed. It will attach to either a 6 or 12 volt element. The in dash receiver also must be changed. GM made a slight difference in element diameters so 6 and 12 volt units. An owner in later years could not accidentally mix the two different voltage types.
1954-1955 Example (above)