there are two "1" wire units. The top one, is the water temp sender for the gauge. The lower "1" wire connecter is the A/C switch which switches to ground at 160 deg to turn on the auxilary fans when the a/c is on. This connector can be used as the ground for aftermarket fans, eliminating the need for expensive thermostatic control relays. Just give the fan fused power, and ground it to the a/c switch. When the coolent reaches 160, the fan will kick on.
-Jake