From the Boutique:

Frame and Engine Number Designations

Frame ID Numbers - 2001 -present
Example: 1HD1CKM115K012345

1  = Made in U.S.A.
HD = Harley Davidson
1  = Weight Class
     1 = Heavyweight
     4 = Lightweight
     8 = Sidecar
CK = Model Designation
     CA = XLH 883 or 1200
     CE = XLH 883 Hugger
     CG = XLH 1200 Custom
     CH = XLH 1200 Sport
     CJ = XLH 883 Custom
     CK = XLH 883R
M  = Engine Displacement
     M = 883 Evolution XL
     P = 1200 Evolution XL
1  = Introduction Date
     1 = Regular Introduction
     2 = Mid-Year (January)
     3 = California Special
     4 = Daytona (March)
1  = Check Digit
5  = Model Year
     1 = 2001
     2 = 2002
     3 = 2003
     4 = 2004
     5 = 2005
     6 = 2006

Y  = Plant of Manufacture (York, PA)
T  = Plant of Manufacture (Tomahawk, WI)
J  = Plant of Manufacture (Milwaukee, WI)
K  = Plant of Manufacture (Kansas City, KS)

012345 = Sequential Serial Number


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Frame ID Numbers - 1981 thru 2000
Example: 1HD1CAH11BY013278

1  = Made in U.S.A.
HD = Harley Davidson
1  = Weight Class
     1 = Heavyweight
     4 = Lightweight
     8 = Sidecar
CA = Model Designation
     CA = XLH
          XLH 1000cc 1981 - 1985
          XLH 883 1986 - 1987
          XLH 883 Deluxe
          XLH 1100
          XLH 883 1988 - present
          XLH 1200
     CB = XLS 1981 - 1985
     CC = XLX 1981 - 1985
     CD = XR-1000, 1983 - 1985
     CE = XLH 883 Hugger 1987 - present
     CF = XLH 883 Deluxe 1988 - present
     CG = XLH 1200 Custom
     CH = XLH 1200 Sport
K  = Engine Displacement
     H = 1000 Ironhead XL
     L = 1340 Evolution
     M = 883 Evolution XL
     N = 1100 Evolution XL
     P = 1200 Evolution XL
1  = Introduction Date
     1 = Regular Introduction
     2 = Mid-Year (January)
     3 = California Special
     4 = Daytona (March)
1  = Check Digit
B  = Model Year
     B = 1981     C = 1982
     D = 1983     E = 1984
     F = 1985     G = 1986
     H = 1987     J = 1988
     K = 1989     L = 1990
     M = 1991     N = 1992
     P = 1993     R = 1994
     S = 1995     T = 1996
     V = 1997     W = 1998
     X = 1999     Y = 2000

Y  = Plant of Manufacture (York, PA)
T  = Plant of Manufacture (Tomahawk, WI)
J  = Plant of Manufacture (Milwaukee, WI)
K  = Kansas City, KS

013278 = Sequential Number


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Frame ID Numbers - 1970-1980
Motorcycle Serial Numbers
Vehicle Identification Number (V.I.N.) is located 
on the engine crankcase and is the same as the
number located on frame steering head.

Example: 3A 13478 H7
3A = Model Designation
     3A = XLH
     4A = XLCH
     7F = XLCR
     2G = XLT
     4E = XLS


13478 = Sequential Number

H = Decade Code
    H = 1970 thru 1979
    J = 1980 only

7 = Model Season
    0 = 1970
    1 = 1971
    2 = 1972
    3 = 1973
    4 = 1974
    5 = 1975
    6 = 1976
    7 = 1977
    8 = 1978
    9 = 1979


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Crankcase Identification Numbers
Numbers located on both left and right crankcase 
halves.

XL Models: Left Case - Inside, Primary Compartment
           Right Case - Outside, Near Oil Pump

Example: 781 321 007

7 = Engine Designation
     7 = 1000cc Iron XL
     16 = XR-1000
     17 = 883cc Evolution XL
     18 = 1100cc Evolution XL
     19 = 1200cc Evolution XL
     20 = 1340cc Evolution, California (1988 - *)
     21 = 883cc Evolution XL, California (1988 - *)
     22 = 1200cc Evolution XL, California (1988 - *)

81 = Model Year

321 = Day of Production
      001 = Jan. 1st        182 = Jul. 1st
      032 = Feb. 1st        213 = Aug. 1st
      060 = Mar. 1st        244 = Sep. 1st
      091 = Apr. 1st        274 = Oct. 1st
      121 = May  1st        305 = Nov. 1st
      152 = Jun. 1st        335 = Dec. 1st

007 = Number That Day