Small Engines (Lawn Mowers, etc.): safety switches, safety switches, safety module

Question
I have a Murray riding mower, I have replaced two of the three safety switches and had the third tested. However every time I release the clutch or engage the blades the mower shuts off.  It changes gears without problems and the blades engage without problem.  I have checked all of the belts and lines to make sure everything is clear of obstruction.  What can it be???

Answer
Without seeing the wiring diagram I would say the key switch or the PTO switch.. Is there a safety module on the tractor?  It would be a switch that wires go to but does not seem to be activated by anything.  If so this could be bad too.  These are proprietary to the tractor manufacturer so you have to get one from a Murray dealer.