Finished my non-navigation conversion this weekend. The wiring was a bit of a pain, but mostly just because of trying to untangle the wires in the harness inside the small area under the dash.
I used the PAC RP4.2-TY11 to interface my Pioneer double-DIN headunit with the ML amplifier. That works perfectly, although you do lose the ability to use the fader controls, and the auto EQ and time alignment in the headunit (because only the front channels are sent to the ML amplifier). The PAC RP4.2 harness is quite bulky so I spent a lot of extra time depinning it and removing the wires and connectors not used in the GX.
The trim piece for the climate control is a discontinued part so I had to use an aftermarket trim piece from Aliexpress. Unfortunately, they only came in black, which doesn't match the OEM gray. The aftermarket piece doesn't fit very well and doesn't align with the buttons perfectly, so a few of the buttons rub against the trim and can get stuck. Also, the top part of the aftermarket trim doesn't align well with the Metra double-DIN trim from Crutchfield. There is a decent gap between the Metra piece and the climate control. I ended up using the aftermarket black trim for both the climate control and the double-DIN.
While I had the climate control unit out, I also changed the linear polarization film on the display to invert it. Looks a bit less dated.
I wired the reverse camera to the factory rearview camera at the "television" ECU on the right side of the passenger footwell.
View attachment 2748524
the part number of the glass for the climate control frame: 83911-60010