The first two digits indicate year. The letter is the decade;
A = '40s
B = '50s
C = '60s
D = '70s
E = '80s
F = '90s
G = '00s
The third digit designates body line;
A = Ford full size
D = Falcon
E = Escort
F = Pinto, Maverick, Falcon
G = Early Comets, Montego, Cyclone
H = Medium/Heavy Duty Truck
K = Edsel
L = Lincoln Mark VII
M = Mercury
O = Fairlane
R = Capri
S = Thunderbird
T = Pick-up Truck or Bronco
U = Econoline Van
V = Lincoln
W = Cougar
Z = Mustang
{there are actually many more}
The fourth position signifies Engineering group;
A = Chassis
B = Body
E = Engine
If it's a Service Replacement part;
Z = Ford Division
Y = Lincoln-Mercury
X = Original Muscle Parts program
M = Ford Motorsport, SVO, FFRP
The center number, four or more numbers or letters, is the part number. The A at the end of the number indicates that the part is the first version. If it was revised once, it would be B. If it was revised again, it would be C, and so on. When they run out of letters, it becomes AA, AB, and so on.
So if we decode this number, D1ZZ-6675-C, we come up with the
following:
D1 = 1971 model year.
Z = Mustang.
Z = Ford Division Service Replacement part.
6675 = the group number for oil pans.
C = The third version of this part.