fuel sending unit wiring question

I have looked at previous threads but not found the answer I need.
I have a late model sending unit with the return line through it. I have autometer gauges. The gas gauge has not been working so I looked at the sender and have a wiring question. There are three wires (white, black and yellow) at the sender but only the white and black are hooked up. I dont even see a place to hook up the yellow. Can someone tell me what the three wires are for and what order do they hook up?
Thaks

12/21/086:52 PM

Original Post

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