Thanks for replying Wayno. Yep checked it, its not OEM, its a "OE direct replacement" ignition switch for an 82, and while it doesnt have the entire steering lock mechanism, it does look very similar to the back of your switch. the closest wrecking yard with an 82 is a 2.5 hour drive for me, so id like to try and use the swtich i have since i can't return it, and dont want to make the drive unless i have to.
You said the wiring diagram has only 4 wires, but in your photo i see 5 connections on the switch, i assume one is splitting? also, I can see most of the markings on the back of your switch, that should point me in the right direction, is that an S in the top left?