NO salvage yards around. I have a wiring diagram..from Partstree.com Simplicity doesn't stock the harness anymore. tractor to old. have tried crossing with different models, but always different.
http://bsintek.basco.com/BriggsDocumentDisplay/ifDzFO9buG1sF4DHa6lEP5NRQpe.pdf
Your original wiring harness is not your problem. Carefully inspect your original harness visually and hands on. I would be looking for exposed wire and feeling for a broken wire inside the harness. Make sure all connections are clean and install harness making sure harness is secure and not chafing anywhere. Make sure all ground straps and wires are clean and tight. Adjust valves on engine and also adjust air gap at electric clutch, page 42.