406 Auto Dim Rear View Mirror

[Rob Turbo 3]

I fitted a 406 auto dim rear view mirror to my 306 today but I don't think it's working (I'm having no luck with this car lately!) It's dark outside now so I thought I'd give it a try, sat in the car, turned ignition on, pressed the auto button, the green light came on, I aimed a torch at the light sensor and nothing happened! It wasn't the brightest of torches but surely it should have at least dimmed a bit?

 

It's one of the later mirrors with 3 wires, I believe thats an earth, a switched live and a reverse sensor, the wires are green/yellow, blue and purple, no visible numbers on them. Is the green light supposed to come on when the auto button is pressed or should that only come on when in 'reverse mode'?

 

Thanks,

Rob