I've searched for an answer to this question and havent seen an exact answer.

The first thing I did for my home audio was run speaker wire through the attic (16 guage). Come to find out my receiver does not have a speaker wire out for the sub. Is there a way to connect RCA's to speaker wire. Another possible problem is the receiver only has 1 out for the sub, I'm assuming this must be the left side? But the sub has input's for R and L. Will this be a problem?

Thanks for any help

Just use an RCA cable and connect the sub out from the receiver to just one of the sub RCA inputs. The signal is not stereo so you do not need to connect both L and R on the sub for it to work correctly.

Can you pull a coax (aka RCA) cable with the speaker cable that you ran? If not, well, it's problematic. Yes, you can solder RCAs to the end of the speaker cable, and it MAY work. But it is not advisable. And, yes, you only need to connect either the sub's R or L input.

Did you run 2-channels of speaker wire for the sub?