I´m pretty sure your 90 is the same as my 88.
Left front speaker Green / return black and yellow
right front White / return black
Left rear Green with a tracer / return black with a tracer
Right rear White with a tracer/ return black
Red and tan is constant power (memory, electronically tuned radio only)
Violet and orange is power from key
Grey is to the power antenna relay
Blue is dim display signal (electronically tuned radio only)
Orange and white is panel intensity imput (lights)
Black is ground