[Chris616]

The loop will need to be cut in the centre to do some testing with a multimeter to confirm which cable is which. My hunch is there is one cable that runs from the door sensor location on the right side to the door sensor location on the left side (it looks like it might be surface mounted). The looped cable runs from the door sensor location on the left side to the door opener location then terminates beside the person door between the garage and house. If they didn’t leave you a clue where that is, it would make sense to be on the door handle side of the door, but some exploratory surgery behind the drywall may be required to find the wire.

Chris

 

[Norm202]

FWIW...If it were me I would just abandon the existing wire and just string new wire for the safety sensors.