need help with radiator fan sensor wiring?

[dridgy]

I have a 81 model bus with the old type radiator, ie the one with two seperate fan sensors and 2 wires going to each one, one sensor is slow fan speed the other is high fan speed.
My rad got blocked and i was unable to get a replacement early rad so i have had to go for the later model rad which has one fan sensor that has both slow and high fan speeds built into it , also it has three wires going to it and not four.

Does anyone know how i use my original four wires to hook up to the new three wire sensor?

im sure someone must have done this already?

Please help

Thanks

John