Be advised that incorrectly wiring battery voltage into many outboard models engine shutoff circuits will likely fry the ignition system either disabling all spark, erratic spark, or the engine won't shut off spark when turned off.
You might have to fork out the money to replace the switchbox/powerpack. Don't spend any money on parts until the matter is fully diagnosed correctly.
FYI, this is a boat engine issue topic that would be in the Evinrude/Johnson outboard section from the look at your picture.
For Evinrude/Johnson around your year model for the key wires:
Yellow/Black striped is the kill circuit wire that goes to the ignition system.
Black is the ground wire.
Red/purple is the 12V supply from the outboard to the key.
Purple is the 12V supply that is turned on/off at the key that goes to the accessories it is attached to and back to the outboard to enable certain items (rectifier/regulator).
Purple striped white is the choke/primer solenoid 12V that enables these as long as the key is held pushed in.
Please do your homework and verify these things before changing things on your own outboard as the wiring situation on your boat might not completely match what is stated if it has been modified.
If the motor won't shut off even if you manually ground the kill circuit at the powerpack, the only options you have to shut it off are disconnect the gas and let it run out (not a good idea if the motor has oil injection), get the engine to low idle and turn the primer solenoid red lever to dump extra gas in the motor until it floods and dies, or get something to insulate your hands and pull all three spark plugs.
