[Wyllliam]

Originally Posted by Gir

The 28 and 16 pin ones weren't even connected on my car, but all the cabling and plugs where attached to the loom. My car had Bluetooth (no external mic) and USB/AUX built into the headunit, so that might be a possibility.

As far as ISO harnesses, anything designed for a toyota after 1987 should work. The Metra 70-1761 is perfect, and plugs into the stock loom no problem. (Amazon.com: Metra 70-1761 Radio Wiring Harness For Toyota 87-Up Power 4 Speaker: Car Electronics)

The 28 pin connector is for AUX, steering switches (not installed on GT86), microphone, speed signel, reverse signal (for back camera) and the ignition signal.

The 16 pin connector is for the backcamera connection.