2006 supra 21v amp

i have a 2006 supra launch 21v, it has the 4 speakers on the tower and 6 in the boat. it has a 4 channel amp but only the tower speakers are hooked up to channel A and nothing on channel B whats the reason behind this? are the 4 back speakers in the boat also hooked in w/ the tower speaker, and only the front to ran off the head unit or all 6 in the boat to the head unit?

The 6 boat speakers are running off the head unit. In order to get tower speakers the factory requires a amp. Most dealers will order a 4 channel amp instead of a 2 channel so you have the option of running a sub.
So get a small sub and run it off channel B. Factory is a free air kenwood 10 inch but it will sound much better if you get a 12 sealed box spray some undercoating on the box and place it under the steering wheel.

I have 2006 supra 21v

the other b channel is for the optional 10 inch sub which it sounds like you didn't get.

the wiring is not done well in the supra. I had to get it all redone.

My 6 inboard and 4 tower speakers were all going to the a channel and my b channel had the stock sub. this sucked for two reason. overload the a channel amp obviously and second I couldn't just turn on the tower and leave the cabin speakers off.

so I got it all rewired and seperated out so I can fade to the tower or cabin speakers independantly. I added an amp as well and now this is my setup. 4 tower speakers on channel A - the sub is on channel B and a new amp powering the inboard speakers. That all together including the alphine amp costed $750 bucks because they had to rewire everything.