2004 Ford explorer. Heater blowing cold air.

My heater will only blow cold air but I've gone under the
center console and manually switched it over and it will
blow hot air. I've gone under the hood and both hoses are
hot. The heater will actually work if switched over
manually by hand under the center console. I've tried a
wire to it and been able to pull it to kick it on but the wire
always falls off after so essentially it's a one time use kind
of thing. What can it be