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A Jeep VIN changed shape three times: a Willys/Kaiser serial, an AMC-era 13-character code, and the 17-character standard used since the 1981 model year. This reader detects which one you have and explains every position.
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The reference
Pre-1971 · Willys & Kaiser
No standardized structure. A serial encodes cylinder count, model, year, and series in a scheme that varies by model. On WWII and early civilian Jeeps the frame serial and the body-tub number are separate stampings — if they disagree, the vehicle was likely rebuilt from more than one donor, which is itself useful evidence.
≈1971–1980 · AMC / Jeep Corporation
Manufacturer (J), a single model-year digit, a plant/drivetrain code, a two-character series (CJ-5, CJ-7, Wagoneer, Cherokee SJ …), a GVW class, an engine code, then a sequence. Do not run a modern check-digit test on it — the standardized check digit did not exist yet.
1981–present · Standardized
The ISO 3779 / NHTSA standard: a 3-character manufacturer identifier, a descriptor section, a calculated check digit in position 9, a model-year letter in position 10 that repeats every 30 years, a plant code, and a sequence. This reader calculates and validates the check digit and resolves the year using position 7.
Plate locations vary by era: WWII dash and frame stampings; Willys/Kaiser firewall and frame tags; an AMC-era firewall VIN plus a separate trim/data plate near the master cylinder; and a modern driver-side dash and door-jamb certification label. Deeper detail lives in the methodology and the research corpus.