Default Wiring an external microphone from the bus

Hi

Did someone know how to correctly wire an external mike from the main connector?

I made a few tests with a small capacitor mike with know power and nothing happen (i grouded the car-on wire in advance). With a 1.5 V mike i can hear somethingh but the volume is very low.

I'm thinking that i need somethingh different and maybe with a power supply of 5 V but i don't have any schematic nor i wont to fry the XDA !

Any ideas?

Thanx in advance