I am replacing an old thermostat that had 6 wires. It had W,O,G,R,C,and Y. I reconnected all but the O. I can't find any help where this wire should go or if it should be connected at all.
Please advise. Thanks!

What kind of system do you have? Heat pump? Gas?

I have an electric heating with central air conditioning unit.
Thanks!

Heat pump?

No sir.

Can you provide make/model of your air handler and outdoor unit; old thermostat model number and what color wire the O is and what terminal it was on that old stat.