In some cars, Toyota used a single 15-pin plug harness. Toyota also used a 2-plug harness, one plug had 10 pins, the other 6 pins.
Toyota also used a 2-plug harness for a radio having an external amplifier. It appears this setup had two plugs, 12 and 15 pins.
If your original Toyota harness has a 15-pin plug, and your radio has 2-plugs, 10 and 6 pins. You will need an adaptor. Unfortunately I can only find adapters going from a 15-pin plug to non-connected wires, and the 2-plugs system going to non-connected wires.
These were found at web sites, Ride Revolution and Discount Car Stereo.
As Toyota used the 15-pin plug often, there might be an adapter having plugs at both ends. This would go from the 15 pin plug, to the two plug system. I suggest you call around to car radio places that also do installation and tell them what you have. I am sure they ran into this situation before.
It is also possible to obtain a 15-pin plug with wires and splice this into what you have now. When doing so, don’t assume Toyota used standard wire colors such as red for power. They didn’t.
www.installdr.com has the color codes for a 2-plug (10) and (6) pin harness.
If your situation is differant then what is described, post back.