Check fuses with a DVM or VOM don't just look at them

Parking brake should be set and locked for the X3xx to start.

Check parking brake and seat safety interlock switches.

Have battery load tested- usually free at the auto parts store. 12V to purple solenoid wire when the key is hit and ground to the other small wire? Could be the ECU as well.

First jump directly from battery to starter post. IF starter runs now, you know battery & starter are OK and problem is in wiring or switches, perhaps where the battery ground cable attaches to the frame. IF not, jump from a known good battery (car) to the starter. IF it still doesn't run, then starter problem.

Walt Conner

One thing i need to point out:
NEVER USE A CAR BATTERY TO JUMP START A RIDING MOWER BATTERY!
sorry for the caps but i have seen this on several differernt topics now. lets compare a battery to a balloon: if you fill the balloon with water from the kitchen sink, it fills up nice and easy, now try filling the ballon from a fire hose. a car battery is 550 cold cranking amps and higher whereas most lawn mower batterys are approx 250 CCA.
I do agree with Walt on checking the starter with a jumper cable from positive on the mower battery to the post on the starter. if it spins, the battery and starter are good. when you turn the key to the start position, do you here a click? if so, it is probably a ground issue between the engine and the frame. if not, it is a wiring issue.

Car battery truck battery, tractor battery etc. all have the same VOLTAGE and thus the same potential to push current through the motor.

The point is to check the starter motor to see if it's good or not.
Using a known good battery will do this. If the starter motor is good, you CAN'T use too big of a battery. IF it's BAD, you MIGHT just fry it a bit more thoroughly.

Agree with above, I'd just take the battery out and load test it. Now you will know if it's the battery or you have other problems BUT, I would first get pass the battery.

IMO as long as you connect right and use 12V battery to jump it's not going to hurt anything. The tiny starter motor will pull the required amps to rotate it. Bigger battery the longer you can rotate it. I have used Big rig battery for my car on time cause I didn't have time to fix the altnator utlizing jumper cables from front seat floor board. Thing ran three days till I have time to fix it.