I have pritty much work out ( i think) what all of the numbers and letters mean but am still having a few problems. 94DA-12A650-AF. 94 = year.DA = Auto 12A650= ????? AF =====. What do the last two letters identify??? I also have another ECU ending in FA. What is this? Any help would be great.

I have a 94 wagon GLI and the last two letters are MC

Ok That's 4DAF and the other one ending in FA will be 4DFA.
So it's an EF. Now the suffixes are to do with calibration but unless you know from what car it came it can be difficult to work out.
To give you an example an ED Sprint or GT auto is 2DDA, and the same car in manual is 2DCA.
So clive that makes yours a 4DMC.
Now even though the codes are different they can actually be an update version of the same thing ie the cal. is essentially the same but the data locations may be different. In the case of the 4DMC being from a wagon the diference would be in relation to a LWB vehicle hence it should have a lower speed limiter but is also likely to have other differences related to the heavier vehicle.

Pete.

DA = 'Regular'
DT = Tickford
AFAIK

I've got two for an EL I6 Auto
6DBD and a Cop spec one which I can't remember atm.

What about a 4DCD??