Step 2: Bulb replacement
Remove the case of the radio & extract the bulb (This may be glued in & will need to be eased out).
Notice how in an effort to cut costs, the same coloured wires have been used for both positive & negative connections!
Once the bulb is out, fit the LED in its place (I connected wires to it first to identify the polarity (Flat edge to negative)) along with the resistors & then connect it to the original bulb wires (As I did not have a meter I had to trace the circuit path on the board for + & - connections)
I tested the first part of the mod with standard alkaline batteries to make sure it worked.