External Antenna - Background Info

[TM]

Al et al.,
I have this same problem, but with a twist:

My stock Audi/Bose radio gave great radio reception for AM and FM,
but when I scrapped the Bose system, I found that I now have horrible
reception- my Sony radio pulls in FM acceptably, but AM is nil. I
switched between both antennas and the AM reception is still nil.

I don't care about AM reception except for the fact that locally, the
traffic report comes on an AM station every 10 minutes.

Any ideas why the AM reception was fine with the stock radio but absolutely
non existent with an aftermarket one?

Taka