Offroad-Express

Hey. They can have two aerials. One can be in one of the rear windows, so check for other plugs. Also sometimes there is a factory signal booster that needs to be powered up off the head unit (blue wire) and this wire is also used for putting the aerial up and down.

Cheers,

I believe the factory aerial in the rear window was for either AM or FM and the electric aerial was for the other? This was what my Skyline had, with one in the front screen as well, dumb setup if you ask me, OK for Japan but not here in NZ. Just stick with the electric aerial, or if it is faulty replace it with a rubber one.
As Simon says, there should be a power wire to the electric aerial and this will be able to be connected to the head unit somewhere to power it. I suspect this is why you are not getting reception.

You need to google your head unit to see where the "blue" wire connects for the auto antenna up/down feed.