I don't know much about 3 wires version, but for 2 wires it is just the change in resistance that is sensed. I suspect that 3 wires version has a flip switch that connect one wire to either of other two. What I would do if you can't find any information on the net and aren't up for a new part is to measure resistance with a digital multimeter between various wires while wiggling the buckle. I remember in my case it was still connecting intermittently. Just make sure the wires go to the switch and not to an airbag

hnoes: