I returned to assess the wiring again. I determined that the wire needed to be ran outside and that there was another short in the system. After checking voltage, I determined the system actually had a total of 3 shorts. The thermostat wire going outside, the thermostat wire to the thermostat, and the thermostat itself. I put in a new thermostat and it dropped the voltage on O enough to make it not energize the reversing valve. This means that 2 of the 3 shorts are addressed. We will wait to address the wire run to the thermostat until it causes an issue. With the old thermostat, I was getting 24v on O with the thermostat set to off. With the new thermostat, I am getting 10v. This is not enough to slide the reversing valve, but indicates that a short is still present. I cycled heating and cooling to ensure the reversing valve was going to function correctly. The system is functioning properly upon departure.