I installed a 'stock-looking' '06-'07 Scion T1806 (Pioneer) HU in my '01 Toyota MR2 Spyder convertible. I chose it since it is 2-Din like the original radio, is 'plug-n-play' in any Toyota 1987-on, and it has much better sound, plus a CD-changer jack in the back for a $15 iPod cable. An OEM radio unit is also not as tempting for roof-slashing thieves. I also installed a 3 ch. Kenwood amp and a hidden 8" under-dash sub. The problem I am having is that it will only play CD's if I turn the car off and on. If I switch to radio and then back to the CD player, it doesn't play the CD at all. There are no Error statements, and the amp and speakers work fine with the radio, or when I turn the car off & on with the CD loaded. Something external is triggering something goofy in the internal programing, and I do not know what. The wiring diagrams are identical with the original MR2 and the Scion radios. It also happens when I installed a Scion T1807 radio (which does NOT have the CD-changer/iPod jack), so it is not a bad T1806 unit. Anyone else ever experience something similar? Help!
One thing I did find a solution for is that many people have said the backlight for the radio buttons doesn't work, even though the screen that shows the channels is lit. The Scion HU's light is about 40 micro-LED's, so it is not just a burned-out bulb. The 6-prong aftermarket Toyota male adapter plug harness I purchased to make a harness to go to the amp only had the 4 green & purple wires for the rear speakers, and NOT the needed EIR orange 5th one for the dimmer wire (!!). Since my mono sub only uses the left channel and I have no rear speakers in my 2-seater, I used a purple right channel wire in the dimmer's #5 position and connected it to the dimmer wire. Note that the button backlights only come on when the parking lights or headlights are on. The car's interior dimmer dims BOTH the backlights and the screen. So: make sure your rear speaker radio 6-prong adapter plug also has the orange dimmer wire (Toyota OEM is usually white or white with green stripe), that the car's interior dimmer is turned up, and the headlights are ON (not just the daytime driving lights). The LED button backlights should then work.