Rich, delighted to help with DCC wiring on A and C. 
What I did when I wired up my A class was 
first get the brass detail kit from SSM, which 
has the nice little details such as cow catcher 
and radiator grills.This is optional, and you will 
get away without it.I have used the TCS-T1 decoder 
which is 2 function and you can have directional 
lights.You will need to drill out the headlights on 
both ends of cabs.When you get LEDs you will 
also normally need two 1k ohm resistors. 
The TCS decoder has a wire loom that's 
Is colour coded, and this is hard wired into 
the loco.The decoder can be removed from 
harness if need. 
Another option is to use a Hornby Deltic 
chassis which is cut to suit the A class and 
already has a 8 pin connector so you can put 
in a 8 pin decoder of choice.If you want directional 
light there is a common diagram that is used for this. 
I can't remember it off hand but I will get  
back to you.Check out the very early pages 
of my workbench as you will see work on a39 
at that time.