> If this happened right after the alarm install, the installer could have mistaken the lamp wire as a ground. It is easily done, i accidentally did this to my mates car, while installing a stereo head unit. When the lamps are off the wire measures as ground, but when you turn the lamps on the fuse blows as wire becomes live.
> If you recently installed a head unit - read above
> Always replace the fuse with it's correctly marked rating. Fuses are there to protect the wirng, the last thing you want to do is to rewire you car.
Hope that helps
PS: If you are uncapable of disconnecting your all power wires to your alarm (inc ground), then go back to your installer, as them to disconnect it, replace the fuse and test the lights.