I installed a Temp/Compass mirror from a 2000 GM vehicle (got off E-Bay) into my 2001 2500HD. The factory wiring harness was alreay in the headliner and mated with the mirror perfectly, so I found the 2 wires under the fuse block under the hood and spliced in the Gentex Temp Sensor that I also got off of E-Bay. The Compass works great, but the Temperature reads -20 F and flashes an Ice warning! I am in South FLorida and it was approx 80 F today! Any ideas what could be wrong?