I am just going to put the specs here and ask someone who knows what they are doing to tell me the best way to wire it. I have tried many ways but keep blowing fuses.
The amp: Rockford Fosgate 400S
100 W X 2 @ 4 Ohms RMS
200 W X 2 @ 2 Ohms RMS
400 W X 1 @ 4 Ohms Bridged RMS
The sub: Eclipse Aluminum 12 DVC
each voice coil is 4 ohm

The only way I see to match the ohms up is to run it 100x2 but I want more power. Is there any other way to wire this up safely with the amp bridged? Thanks!

 

You are correct!
The DVC 4ohm sub can either be wired for 2ohms (parallel) 8 ohms (series). Since the amp is not speced to be bridged down to 2ohms on a single channel it is not preferred. You can go 8ohms but that would be as good as keeping the stock Nissan Blose system. Just wire each coil to one channel.

You only have one sub correct?

 

Yes, just one sub. I figured when I bought this sub that my old amp wouldn't work but I wanted to see what I could get out of it. I will try putting one coil to each channel and see what happens. Thanks for your help!