Source: Federal Reserve Board, Data For 1929-1939: Federal Reserve Bulletin, June 1955, "Estimates Of Consumer Instalment Credit", Table 3; Data For 1940-1959: "Consummer Credit", A Supplement To Banking And Monetary Statistics, Section 16 (New); Data For 1960-1967: Bulletin, December 1968; For 1968: Monthly Bulletins And Frb Monthly Release G-19, "Consumer Credit"
This NBER data series m10046 appears on the NBER website in Chapter 10 at http://www.nber.org/databases/macrohistory/contents/chapter10.html.
NBER Indicator: m10046
Release: NBER Macrohistory Database
National Bureau of Economic Research, Automobile Installment Credit Outstanding for United States [M10046USM144NNBR], retrieved from FRED, Federal Reserve Bank of St. Louis https://research.stlouisfed.org/fred2/series/M10046USM144NNBR/, October 13, 2015.