Just to update this information, it appears there are a second set of of wires going to the rear doors of the H3T for the high range. The rear door speakers are 6x9s. The amp in the H3T with the 6 disc changer is an 8 channel monsoon amp. The wiring diagram on Schwartzys site is mostly bang on. It is possible to fit a 4 channel JL amp in the factory location of the H3T without relocating it to under the seat. I had to remove two of the studs from the rear firewall and enlarge two holes slightly on the amp mounting plate to make that happen. You will need to use two nuts to space below the amp.
I recommend running a new set of RCA cables to the rear as there is quite a bit of noise picked up from the factory wires running to the back. This is also the case if only changing the head unit. I had soldered RCA ends in the dash and again at the amp, and there is a noise being picked up from one or all of the CANS in the system. There is extra space under the door sill trim on the passenger side to run all the way to the back.
The amp can be connected without extending speaker wires, without strain. I do recommend using a heavy gauge ground and power lead. I connected the ground to the the stud on the rear firewall with a 6mm nut, then mounted the amp on top of that. The positive lead was easy to fish as there is a vent on the rear firewall, and just below that area is the parking brake cable.
Connecting to the battery was easy also, as there is a free 6mm stud on the cable end. If you have the alpha, be sure to bring the wire up tight to the firewall and fender. The manifold will likely melt the coating off the wire.
The rear speakers in the H3Ts are 6x9s. I think the Metra 82-3004 adapters will work for this but haven’t tried them yet. I have made do with cutting the old speaks apart, pulling the cone off the frame and using that. It does need a little trimming to make this work, but it avoids drilling into the door.
