280 LX won't start. Won't even click or turn over. Battery is fully charged. The trouble shooting manual notes it could be an ignition system fuse, and to contact a Deere serviceman. Is there an in-line fuse, or could we be talking about the solenoid that's attached to the starter motor? Any help would be appreciated.

Gary, Do you mean car will not start, or do you mean it will not turn over. If it does not turn over, even with boost, battery cables bad,starter relay or fuse bad, or starter defective.
Trouble shooting links below.
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Engine Won Crank or Start


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Engine Won Start No Crank Diagnosis Troubleshooting Starting System Issues

if it wont turn over 1st check the ground s on the car and the battery 1st. your battery can be fully charged and the car will not start even over night this can happen. then look at the starter. Note: if you have over 109K on the car and the timing belt has never been replaced you will need to have this checked as well.

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Park neutral safety switch maybe be the reason for the no crank ! Try putting the vehicle in park ,then try to crank the engine . Testing the electrical circuit is the best way to trouble shoot this problem , along with do a voltage drop test on the starter circuit ! This will test the battery cables an connections .
Starter Voltage Drop
How to voltage drop test starter motor circuit
Does it have a manual or automatic transmission ? Manual ? clutch switch . Looking at a wiring diagram I also see a starter cut relay !
http://www.bbbind.com/free_tsb.html Free wiring diagrams . Enter vehicle info. year , make , model and engine size . Under system click engine , under subsystem click starting . Then click the search button , then click the blue link ! Check the starter cut relay also . Videos on youtube showing how to test a relay controlled circuit !

Have you checked the battery terminal connections? Is the battery charged fully? Are you sitting on the seat when you try to crank the mower? Could be any of the above but most likely battery connection or the battery is discharged or old.

ORDER A CLYMER MANUAL FOR YOUR BIKE!!! Everything is easier to inspect with the fairings and accessory covers removed. While you are waiting for the manual, trickle charge your battery. Make sure your charger is a maintainer as well. It charges your battery and keeps it conditioned. Keep in mind, even if it's a new battery, they are not impervious to fault. When you get your manual, two or three days later, the battery should have a full charge as indicated by a green light(normally) on the trickle charger. Now, key your ignition on and get your multimeter. Read for battery voltage on the down side of your ignition switch.Then measure and note the draw from your battery as you hit the start switch. Open your manual and start reading through components like your rectifier, coils, main power fuse (probably a 30A)on your fuse box. Remember, a bad ground within your electrical system will report a failure to allow passable current to the components that need the juice. Look for corrosion or gunk on the contacts of your electrical components. Good luck, let me know how it works out.