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.