Weather king inside electric unit

Question

Hello. The fan will run if the thermostat is set at cool and on. Or cool and auto. The fan will run if put to heat and on but NOT heat and auto. Then we removed the top halfs panel and there was a yellow wire that was hanging lose with no cap on it. There was one wire with a cap made for two wires but only one inside. my husband put the yellow wire in with the red or purple I think and saw smoke shoot out of a little black box on the left side of the panel if looking at it. This box had wires going to it. Now nothing works. It is a 24* night here in Phenix City Al. and we have 4 children. PLEASE PLEASE PLEASE HELP As soon as Possible. Thanks Brandi