i am changing my car stereo and found a device that the roof aerial
connects to, but dont know what it is.

it's about 8.5 cm in length, looks like a silver barrell, aerial lead
goes in one end, out of other end is thick black aerial cable that goes
to stereo & a thin white aerial whic i am not sure where it goes. i am
not sure if the white wire goes to a ground or +12v.

I think it is some knind of amplifier. the white wire was connected to
one of the cd changer terminals on my old stereo.

any help appreciated