What wire for Tranny Temp Gauge??

[wcbcruzer]

I just got an Autometer tranny temp. gauge off my friend. It's brand new but it didn't come with any wire to connect the sending unit to the gauge. In the instructions it says to use 18 gauge wire. I was wondering what length and what kind of wire to buy so it doesn't throw my temp. readings off. Cause the longer the wire, the more resistance; hence, lower temp. readings.. Am I correct? I take it, 18 ga. stranded copper wire is the best? What length/type of wire originally comes with the Autometer temp. gauges?? Thanks for your help...