I found another loose wire

Here is a photo which I've tried to label whats going on



and here are a couple other photos


This is the "loose wire"


Going to the rear relay






Might take it to my mechanic, seems a long shot to get it sorted over a forum.

The terminal the original loose wire is opposite one going into the harness =/ I am not sure what the relay does and I will borrow a multimeter to check whether it has power on ignition but I don't have one ATM.

Any guesses on the plug at the back on the heater core box?

Cheers