The LED's are Nano's from Ngineering. They are .020 x .040"
The ditch lights plug into a socket built into the porch of the loco... a picture is worth a thousand words here...
Drill the holes first, solder wires to small PB tabs, glue under holes, push in light from above.
I also created a contact pad in the nose of the loco so that I didn't have to unsolder the wires everytime I took the shell off.