radio installation antenna causes short

Here is a strange one. I installed a stereo head into my mazda (sorry but it may have general interest too) and it works fine until I plug in the antenna lead. then it blows my 10A dash/taillight fuse! This is very strange. I ohmed out the antenna, it has no short between the center conductor and the ground sheathing, its only tightened to my fender, not an active antenna. I probed the antenna socket on the radio, the socket is grounded with the chassis and there is only .11v on the center contact. There is no continuity between the antenna socket and the center conductor. It works fine with the unit on AUX (no antenna installed) but as soon as I connect antenna, it blows fuse?? It has its own 15A fuse but it runs through a 10A circuit. Should I up the 10A to 15A or just run a dedicated power lead to battery? I liked the harness connection becasue the radio would turn off with key. Oh, and this radio (Boss 612UA) has dismal PLL signal lock, it will drift (treble comes and goes like the speakers are going underwater) while sitting at a light as well as on the road but only when using radio (with no dash or taillights...)