Small Engines (Lawn Mowers, etc.): Snapper lawn mower no start, snapper riding mower, snapper lawn mower

Question
Eric:
My neighbor has an older rear engine snapper riding mower with a 10hp electronic ignition Briggs engine that will not start. He has replaced the coil and I replaced the ignition switch. The only way I could get it started was to disconnect the wires on the shifter safety switch and hook them together. The engine started but would not cut off , I then connected the switch back up and it started and cut off with the ignition switch. My neighbor then took the mower home and cut his grass , cut it off and tried to restart after about two hours and almost ran the battery down before it started. Next day would not start at all. Engine getting fuel but no spark. The ignition switch may not have been bad but when I checked with a test light I was getting power on red wire all the time (from battery) Power on blue wire in start position but no power on black wire which appears to supply engine power. Any help would be appreciated as I can fix most things mechanical but sometimes have problems with even simple electrical woes.
                     Thank You
                    Ernie Bryant

Answer
The black wire should run to the engine block...near the throttle cable assembly.  Check to make sure.  If this is correct, then the black wire should be "open", infinite resistance, with respect to ground when the key is in the run position.  When you turn the key off the wire should be grounded, no resistance to ground.  Basically you short the primary coil voltage to ground just like taking a screwdriver and shorting the spark plug to ground to cut off the engine.  There should NEVER be any voltage on this wire.

Check the wiring harness.  Several Snappers use a safety interlock device generally mounted near the key switch.  Unfortunately there is no way to check the device.

I would also check  the safety switches with and ohm meter.  The switches should show open and closed like a light switch.  You may want to clean the connections.

Let me know if you find the interlock device and about the black wire.
Eric