Installed small sub and amp.. problem.

I just installed an 8" punch p2 sub and 400w kicker amp in my 06 dc. Now I am not unfamiliar with wiring so I am pretty sure it's wired correctly. I did not use a converter box I just tapped into the front speaker wires for signal and ran them to 2 rca adapters. Everything works fine until about volume 40. The stock deck then shuts off. It seems to be a breaker because it resets when I shut my truck off. Sorry if this has already been posted somewhere else I couldn't find it. I'm assuming the solution is a rca converter box but I have done this in other vehicles with success so I'm just curious I guess. Thanks.

 

The impedance at the stock HU is too low and the deck is going into a protection mode. Install a LOC and you will be ok.

 

Figured as much. Thanks for the info.