2001 gs 430 aftermarket radio

I installed a kenwood dnx-5120 double din navigation unit in my car.  My problem is that I had to bypass the factory amp because I could not figure out how to kick it on and stay on.  I don't want to buy another amp to push the factory woofer.  In my current set up my factory amp is not on so my factory subwoofer is not working.  I have hooked up the speakers to the kenwood head unit for power.  If someone knows how to keep the factory amp on I would greatly appeciate it.  I also wanted to know if anyone knows which wire to tap into to make my steering controls work.  I have bought a peripheral steering control adaptor but wanted to know if anyone know which wire it is on the steering column to tap into.