Ford Escort MK2 (1979) Starter motor

So I have got to the stage of wiring the starter solenoid and I have Multiple wires and cables that I have to attach.
I have the:
 
Main + form the battery 
Alternator +
Ignition Cable 
1 spade plug
1 other unknown wire, running along with ignition wire 
 
 
Image below is the solenoid close up 

Imagine below is from the front of the car.