Temp gauge problems.

I'm having problems with my either temperature gauge, my temperature sender, or the wire running to gauge and sender. I'm really clueless as to what is wrong. I just know that my temperature gauge stays below cold constantly. How do I test it or what should I test first? My gas gauge works fine. My oil pressure light is also out. I did end up hooking up the battery backwards On accident. I'm really just clueless on where to start testing and how to test it. Again all lights, blinkers, wipers, and gauges work except for the temp gauge and the oil pressure light.