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you need 3 wires for this to work....is there another unused wire in the cable?
now first...the red goes to R, the white goes to W...the blue we will put on C.
But 2 things...
1 - the blue wire at other end in furnace must be attached to a C (or if trane possibly a B)
and 2 - wiring white to C would have shorted the low voltage system.
Can you give me model number of the indoor furnace?