The Temp/Oil gauge for my 1971 240Z has become wonky.  I've cleaned the (yellow) wire's bullet connector to the water temp sender. However, in the same loom, there was a black wire with an unused female spade connector.  Does someone know the purpose of this connector and what it should be attached to?  Have I broken a circuit to...something?  

The spade connects to a condenser on the back side of the distributor.

Jim, thanks!  Nice looking 240Z BTW.