Jason
The single red wire should run to a ( pressure switch ) at the hydraulic lift cylinder each cylinder should have one .
The controller uses these pressure switches to balance the lifting action in case one Jack has to travel farther to the ground
The switches are normally open and close at 140 PSI .
I don't think the lost of a pressure switch wire would keep the system from working at all.
I think you have another issue
First check your control panel to figure out which model system you have the go to HWHs web site technical library and follow the manuals troubleshooting section for you model it should walk you through the diagnosis.
https://www.rvtechlibrary.com/chassis/leveling.phpHope this helps
Eric