Oxygen sensor going nowhere
 

Hi all,
Just bought a EURO 280SL, M110 motor, and seems that a lot of the electrical has been tempered with (tons of cut wires, looking like alar has been removed, and electronic boxes inside the car suggesting third-parts fuel economy gadgets.
Car is anyway running with a high idle problem.
Anyhow, today I wanted to change the oxygen sensor, that being part of a program of changing tons of stuff, and I discovered that the previous sensor wire was leading... nowhere. I looked for the other part of the cut wire, and couldn't find it anywhere.

Anyone could let me know where it should go? Photo would help. Thanks a lot!

By the way, it's a 1985