SOLVED

I think

Throw a 10k resistor from the serial pin to ground. The question now is, should that resistor remain even after I actually hook up the serial signal from the other device?

[PC - USB > serial] ---> [Main Board (PCCLD)] ---> {1 way serial} ---> [New/Master PIC]

Should that resistor remain, or can I turf it once I hook up the serial?