Need help troubleshooting stereo problems - 2009 Sierra
 

2009 Sierra SLT, came with Bose
Prior to yesterday, I had JVC HU, Swag 6.5s, factory sub and amp, Kicker 8L5 with cheap Dual Amp

Yesterday I removed the Kicker 8L5 and cheap amp, replaced with two Kicker 8L7s and a Pioneer 800W amp. I put one under the back seat and the other is in a stealth box under the console. In doing this, I had to remove the factory Bose sub under the console. I retained the factory Bose amp and reconnected the big modular plug that goes to it. The only thing that didn't get connected was the small modular plug that went to the factory Bose sub.

Now, a song will start to play, and within 5 seconds it cuts to half volume (all speakers). It's going into some sort of safe/protect mode and I don't know enough about it to troubleshoot it.

Any ideas?

Look for a wiring diagram for that system. There's one floating around. I removed that amplifier on my suburban when I removed the console for a jump seat and swapped head unit. I had to use the wiring diagram to rewire the harness from line-level to speaker-level since the heat unit didn't need the amplifier.

You may have a short in the speaker wiring. Use the balance/fade to see if you can isolate it that way. Or use the diagram to check speaker impedance at the connectors with a DVOM by backprobing the connectors.