Bear with me here lol. I recently installed a MB Quart NAU460 4 channel amp, Zapco AG360, 4 MB Quart 6.5"speakers, and 2 polk 10" subs. Had the MB on the subs temporarily and the Zapco on the interior speakers. After one day of use the subs stopped playing and the MB amp is in protect mode. I hook the Zapco up to the MB wiring and the subs work once again so something must be toast in the MB amp right. So I exchange the amp for another one and go to install last weekend and switch the amps so the MB is now running the interior speakers and the Zapco is running the subs. As soon as I hook up the "new" MB amp it goes directly into protect mode again, WTF? So I have a really really old school alpine amp and I hook it up and it runs the interior speakers fine and the system works great, hook up the MB again and nothing. So I get back from the river and decide this morning to first hook the amp directly to the battery and low and behold no protect mode, WTF? Hook up RCA's and some speakers and it works fine. Anyone have any idea why I would be having this problem? Why would my Zapco and Alpine amps work but not the MB in the boat but the MB works outside of the boat. Only thing I can think of is could it have anything to do with the fact I am running both amps off one remote wire from the head unit? Also why would it work before and not now. I need help, I am getting so frustrated. Thanks guys.