A somewhat easy find and fix.
When you do your walk-around, you see this....
When you power-up, you see this....
The ground signal for ECAM landing light extended comes from the light assembly itself. The left and right lights are wired in parallel. You've got a 50-50 chance when you take the first "can" plug off.
It's a real quick repair. About 10 screws and out she comes.
New light extended....
A300-600
ASM 33-42-00
IPC 33-42-03-01
AMM 33-42-21-04