OK, I have an Alpine SWR-1021D which 2 + 2 ohm. In the manual it shows how to connect to an amp at 4 ohm. It shows how to connect (2) subs at 2ohm. But how would you wire 1 amp and 1 sub to run a 2Ohm. Below is what it shows in the manual.
Thanks for any help.

 

You need a dual 4 ohm sub (wired in parallel) to make a 2 ohm load. If your amp is a bridgeable amp and you have it bridged, you should be using a 4 ohm load, because it is likely that 2 ohms bridged would kill your amp.