It's been about a month since my double din install. All of a sudden my tail light fuse blows as soon as I click on the headlight switch. Even if the car or stereo is off and I just click on the headlight ,it pops the fuse. The only thing I've done from stock is the JDM DD , should I assume that's what is the cause and rip into the damn dash again to check all wiring and grounds? Even though it was fine for a month?

 

What year is your vehicle? Has it been in any accidents or has anything else changed (besides the head unit)? How was the new head unit connected to the factory radio?

It is possible for bulbs to short out. Since the tail lights were working fine for a month after the install of the radio I would not automatically jump to the radio as being the cause (as long as the installation was done to professional standards - if you wire nutted the wires together I would go right to the radio first!)