Thanks for the information - It looks like my Starter Solenoid was stuck open. Luckily I had a new one laying around so I switched it out and fixed that problem. I must have cooked it when using a screwdriver to start the car touching the battery to ignition bolt on the solenoid.

Unfortunately now my original problem is still there. When I turn the key it wont start. If I bypass using a screwdriver from the positive battery to the ignition bolt on the solenoid the car starts. He is the important part - when I put the harness wire back onto solenoid after it starts then the car turns off.

Could it be that some functions of my headlight switch are bad?
Does this power some parts of the harness?

Thanks in advance

PS - I tried to upload diagrams of the two harnesses for future reference but the file size is apparently too big.