I recently changed the factory radio to an aftermarket radio. After the installation was done i noticed that the dash lights and the tail lights were not working. the fuse was blown and when i replaced it it blowed again. i got a volt meter and checked continuity. there is 12v on the primary, but when i turn the swith on the secondary goes to ground. i removed all the lights and still no change. i unhooked the new radio and still no change. any ideas?