My mum has a Citroen Berlingo and she says if the headlights are on, the indicators don’t work. If the headlights are off the indicators works fine.
Does anyone know why this is happening?
Sounds like a poor ground, when the headlights are off then the 21W can get to ground via the headlamps but if the headlamps are on then that does not happen.
Check the ground connections and for breaks in the ground wires.