Just had a quick search for 96 model rav4 o2 sensor and it comes up being a 2 wire replacement, although the 98model is a 4 wire.
Have you checked yours is a 4 wire?
You can test for these wires easily using a multimeter, the heater should be 12v, sensor earth - test continunity with the chassis and the wire, signal will make a small voltage somewhere around 0.1v and when hot 0.6v, and the other is heater ground which will not matter which earth is which as there both earthing.
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