Craftman mower won't start with the key

[Nick Weber]

I am not sure what model we have. Bought it used. It does have a 15 hp Briggs and a 42 inch cut. It won't start with the key. I can jump the solenoid and it will start, as long as the clutch is locked down. When it first started acting up, it almost acted like it wasn't getting full 12 volts to the starter. Almost like an intermittent short to the point where the starter would disengage momentarily, then reengage. Now there is nothing to the starter with the key. Amp gauge still registers when you turn the key off or on.
I assume that I have a safety bad, but NO CLUE how to check the circuit. The clutch safety works, I guess. It won't start, if the pedal isn't locked down.

Thanks

 

[ILENGINE]

You will need to check the battery connections to make sure they are clean and tight. Check for corrosion of the ground wire at the point where it connects to the frame. Check for corroded terminals on the key switch, the pto safety switch/electric pto switch, and the clutch switch. After than you will need to start testing the switches for resistance and see if you have a faulty switch.