W203 confusing cigar lighter socket problem

[Littledigger]

I installed an extra cigar lighter socket in the ash tray compartment by tapping into the wiring for the socket in the cup holder compartment.

I inserted the USB charger into the new socket and the led lit up to say it was powered (great) so i plugged my iPhone in and also plugged it into the Aux to test it, and i get a slight buzzing noise when listening to music. OK, disconnected the USB and the buzzing stopped. plugged the USB cable into the factory socket and no buzzing, so I took the USB charger out of the factory socket and put it into the new socket and the LED won't light and it won't charge the iPhone

Can anyone shed some light on this, what am I doing wrong?

cheers

 

[Littledigger]

Does anyone know where the live wire goes on the socket? Is it to the centre of the socket or is it to the edge?

 

[fuzzer]

The Centre is the live and the ourside is the earth. Sounds like bad joint at the original socket. How did you tap in?

 

[Littledigger]

I tapped in using a connection block.