automoter water temp!!!

Just trying to verify before buying it but is this the right part for the temperature sender? Looking on RockAuto this is the number that came up when matching to the GM part number.
ACDELCO Part # 213815

I plan on running the gauge soon but need to replace the ECT sensor now. Would I be safe to assume that, after installing the new sensor and plug, if I just use the two wires for the PCM and leave the 3rd alone I will be fine? Basically like having the 3rd wire dangling free and not connected to anything?... Until I get the gauge hooked up anyways. Rather than getting an ECT for an Impala now then later on buying and replacing a new sensor for the F-Body.

Just for some clarification before someone questions my antics... I am doing some diagnosing with my car right now and that is one of the parts I am going to be changing. I'm not going to be driving it with that wire dangling, I just don't have the new gauges hooked up and want to make sure it's going to be running right.