My subs in the rear sometimes work and sometimes dont.. I tried another amp and still is the same, subs are still new too.. was guessing its the head unit having the problem, any suggestions, thanks.

 

RCA cables or remote wire.

I had the EXACT problem. If I'd whack my dash on my side of the head unit, they'd come back on then cut out again.. I bought new RCA's and rerouted a new remote wire, and it still did it. My RCA jacks ended up being the culprit on my Pioneer DEH-P6400. I just switched them to the FT OUT set of RCA's.. No problem now

Take the remote wire and run another NEW wire inside the cab, or reroute the old one to where you can see it or touch it.. Just temporary to help you figure out if it is that or not. (possibly arcing to ground or a cut section of wire.)

I'll be replacing the head unit w/ a DVD player soon... I want to run multiple amps.